Wireless energy distribution system

ABSTRACT

Described herein are systems for wireless energy transfer distribution over a defined area. Energy may be distributed over the area via a plurality of repeater, source, and device resonators. The resonators within the area may be tunable and the distribution of energy or magnetic fields within the area may be configured depending on device position and power needs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Appl. No.61/382,806 filed Sep. 14, 2010.

This application is a continuation-in-part of U.S. Ser. No. 13/222,915filed Aug. 31, 2011 which claims the benefit of U.S. Provisional Appl.No. 61/378,600 filed Aug. 31, 2010 and U.S. Provisional Appl. No.61/411,490 filed Nov. 9, 2010.

The Ser. No. 13/222,915 application is a continuation-in-part of U.S.Ser. No. 13/154,131 filed Jun. 6, 2011 which claims the benefit of U.S.Provisional Appl. No. 61/351,492 filed Jun. 4, 2010.

The Ser. No. 13/154,131 application is a continuation-in-part of U.S.Ser. No. 13/090,369 filed Apr. 20, 2011 which claims the benefit of U.S.Provisional Appl. No. 61/326,051 filed Apr. 20, 2010.

The Ser. No. 13/090,369 application is a continuation-in-part of U.S.patent application Ser. No. 13/021,965 filed Feb. 7, 2011 which is acontinuation-in-part of U.S. patent application Ser. No. 12/986,018filed Jan. 6, 2011, which claims the benefit of U.S. Provisional Appl.No. 61/292,768 filed Jan. 6, 2010.

The Ser. No. 13/154,131 application is also a continuation-in-part ofU.S. patent application Ser. No. 12/986,018 filed Jan. 6, 2011 whichclaims the benefit of U.S. Provisional Appl. No. U.S. 61/292,768 filedJan. 6, 2010.

The Ser. No. 12/986,018 application is a continuation-in-part of U.S.patent application Ser. No. 12/789,611 filed May 28, 2010.

The Ser. No. 12/789,611 application is a continuation-in-part of U.S.patent application Ser. No. 12/770,137 filed Apr. 29, 2010 which claimsthe benefit of U.S. Provisional Application No. 61/173,747 filed Apr.29, 2009.

The Ser. No. 12/770,137 application is a continuation-in-part of U.S.application Ser. No. 12/767,633 filed Apr. 26, 2010, which claims thebenefit of U.S. Provisional Application No. 61/172,633 filed. Apr. 24,2009.

Application Ser. No. 12/767,633 is a continuation-in-part of U.S.application Ser. No. 12/759,047 filed Apr. 13, 2010 which is acontinuation-in-part of U.S. application Ser. No. 12/757,716 filed Apr.9, 2010, which is a continuation-in-part of U.S. application Ser. No.12/749,571 filed Mar. 30, 2010.

The Ser. No. 12/749,571 application is a continuation-in-part of thefollowing U.S. applications: U.S. application Ser. No. 12/639,489 filedDec. 16, 2009; U.S. application Ser. No. 12/647,705 filed Dec. 28, 2009,and U.S. application Ser. No. 12/567,716 filed Sep. 25, 2009. U.S.application Ser. No. 12/567,716 claims the benefit of the following U.S.Provisional patent applications: U.S. App. No. 61/100,721 filed Sep. 27,2008; U.S. App. No. 61/108,743 filed Oct. 27, 2008; U.S. App. No.61/147,386 filed Jan. 26, 2009; U.S. App. No. 61/152,086 filed Feb. 12,2009; U.S. App. No. 61/178,508 filed May 15, 2009; U.S. App. No.61/182,768 filed Jun. 1, 2009; U.S. App. No. 61/121,159 filed Dec. 9,2008; U.S. App. No. 61/142,977 filed Jan. 7, 2009; U.S. App. No.61/142,885 filed Jan. 6, 2009; U.S. App. No. 61/142,796 filed Jan. 6,2009; U.S. App. No. 61/142,889 filed Jan. 6, 2009; U.S. App. No.61/142,880 filed Jan. 6, 2009; U.S. App. No. 61/142,818 filed Jan. 6,2009; U.S. App. No. 61/142,887 filed Jan. 6, 2009; U.S. App. No.61/156,764 filed Mar. 2, 2009; U.S. App. No. 61/143,058 filed Jan. 7,2009; U.S. App. No. 61/163,695 filed Mar. 26, 2009; U.S. App. No.61/172,633 filed Apr. 24, 2009; U.S. App. No. 61/169,240 filed Apr. 14,2009, U.S. App. No. 61/173,747 filed Apr. 29, 2009.

The Ser. No. 12/757,716 application is a continuation-in-part of U.S.application Ser. No. 12/721,118 filed Mar. 10, 2010, which is acontinuation-in-part of U.S. application Ser. No. 12/705,582 filed Feb.13, 2010 which claims the benefit of U.S. Provisional Application No.61/152,390 filed Feb. 13, 2009.

Each of the foregoing applications is incorporated herein by referencein its entirety.

BACKGROUND

1. Field

This disclosure relates to wireless energy transfer, methods, systemsand apparati to accomplish such transfer, and applications.

2. Description of the Related Art

Energy distribution over an area to moving devices or devices that maybe often repositioned is unpractical with wired connections. Moving andchanging devices create the possibility of wire tangles, trippinghazards, and the like. Wireless energy transfer over a larger area maybe difficult when the area or region in which devices may be present maybe large compared to the size of the device. Large mismatches in asource and device wireless energy capture modules may pose challenges indelivering enough energy to the devices at a high enough efficiency tomake the implementations practical or may be difficult to deploy.

Therefore a need exists for methods and designs for energy distributionthat is wire free but easy to deploy and configurable while may deliversufficient power to be practical to power many household and industrialdevices.

SUMMARY

Resonators and resonator assemblies may be positioned to distributewireless energy over a larger area. The wireless energy transferresonators and components that may be used have been described in, forexample, in commonly owned U.S. patent application Ser. No. 12/789,611published on Sep. 23, 2010 as U.S. Pat. Pub. No. 2010/0237709 andentitled “RESONATOR ARRAYS FOR WIRELESS ENERGY TRANSFER,” and U.S.patent application Ser. No. 12/722,050 published on Jul. 22, 2010 asU.S. Pat. Pub. No. 2010/0181843 and entitled “WIRELESS ENERGY TRANSFERFOR REFRIGERATOR APPLICATION” the contents of which are incorporated intheir entirety as if fully set forth herein.

In one aspect of the invention repeater resonators are positioned aroundone or more source resonators in a defined area. The one or more sourcemay be coupled to an energy source and generate an oscillating magneticfield which may be transferred to the repeater resonators around thesources, and the repeater resonators may transfer the field to otherrepeaters around them thereby extending the energy over the definedarea. In embodiments energy may be extended over an area of 10 cm² or 2m² or more.

In the distribution system with multiple sources the frequency and phaseof the sources may be synchronized.

In another aspect of the invention the distribution system may usetunable repeaters that may have a tunable resonant frequency or otherparameters. The parameters of the repeaters may dynamically orperiodically adjusted to change the magnetic field distribution withinthe defined area. In embodiments the resonators and components of thesystem may have a communication capability to coordinate tuning andparameter adjustment of the resonators and components of the system toroute or distribute the energy to specific areas of the defined area orroute the energy along a specific route of resonators that may becalculated using network routing algorithms and other methods.

In another aspect the components of the system may be integrated intoflooring material such as tiles and distributed in a room floor or awall or ceiling.

In one more aspect multiple resonators and power and control circuitrymay be incorporated onto one sheet and may be trimmed or cut to fitdesired dimensions.

Unless otherwise indicated, this disclosure uses the terms wirelessenergy transfer, wireless power transfer, wireless power transmission,and the like, interchangeably. Those skilled in the art will understandthat a variety of system architectures may be supported by the widerange of wireless system designs and functionalities described in thisapplication.

This disclosure references certain individual circuit components andelements such as capacitors, inductors, resistors, diodes, transformers,switches and the like; combinations of these elements as networks,topologies, circuits, and the like; and objects that have inherentcharacteristics such as “self-resonant” objects with capacitance orinductance distributed (or partially distributed, as opposed to solelylumped) throughout the entire object. It would be understood by one ofordinary skill in the art that adjusting and controlling variablecomponents within a circuit or network may adjust the performance ofthat circuit or network and that those adjustments may be describedgenerally as tuning, adjusting, matching, correcting, and the like.Other methods to tune or adjust the operating point of the wirelesspower transfer system may be used alone, or in addition to adjustingtunable components such as inductors and capacitors, or banks ofinductors and capacitors. Those skilled in the art will recognize that aparticular topology discussed in this disclosure can be implemented in avariety of other ways.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. In case of conflict withpublications, patent applications, patents, and other referencesmentioned or incorporated herein by reference, the presentspecification, including definitions, will control.

Any of the features described above may be used, alone or incombination, without departing from the scope of this disclosure. Otherfeatures, objects, and advantages of the systems and methods disclosedherein will be apparent from the following detailed description andfigures.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a system block diagram of wireless energy transferconfigurations.

FIGS. 2A-2E are exemplary structures and schematics of simple resonatorstructures.

FIG. 3 is a block diagram of a wireless source with a single-endedamplifier.

FIG. 4 is a block diagram of a wireless source with a differentialamplifier.

FIGS. 5A and 5B are block diagrams of sensing circuits.

FIGS. 6A, 6B, and 6C are block diagrams of a wireless source.

FIG. 7 is a plot showing the effects of a duty cycle on the parametersof an amplifier.

FIG. 8 is a simplified circuit diagram of a wireless power source with aswitching amplifier.

FIG. 9 shows plots of the effects of changes of parameters of a wirelesspower source.

FIG. 10 shows plots of the effects of changes of parameters of awireless power source.

FIGS. 11A, 11B, and 11C are plots showing the effects of changes ofparameters of a wireless power source.

FIG. 12 shows plots of the effects of changes of parameters of awireless power source.

FIG. 13 is a simplified circuit diagram of a wireless energy transfersystem comprising a wireless power source with a switching amplifier anda wireless power device.

FIG. 14 shows plots of the effects of changes of parameters of awireless power source.

FIG. 15 is a diagram of a resonator showing possible nonuniform agneticfield distributions due to irregular spacing between tiles of magneticmaterial.

FIG. 16 is a resonator with an arrangement of tiles in a block ofmagnetic material that may reduce hotspots in the magnetic materialblock.

FIG. 17A is a resonator with a block of magnetic material comprisingsmaller individual tiles and 17B and 17C is the resonator withadditional strips of thermally conductive material used for thermalmanagement.

FIG. 18 is block diagram of a wireless energy transfer system within-band and out-of-band communication channels.

FIG. 19A and FIG. 19B are steps that may be used to verify the energytransfer channel using an out-of-band communication channel.

FIG. 20 is an isometric view of a conductor wire comprising multipleconductor shells.

FIG. 21 is an isometric view of a conductor wire comprising multipleconductor shells.

FIG. 22 is a plot showing the current distributions for a solidconductor wire.

FIG. 23 is a plot showing the current distributions for a conductor wirecomprising 25 conductor shells.

FIG. 24 is a plot showing the current distributions for a conductor wirecomprising 25 conductor shells.

FIG. 25 is plot showing the ratio of the resistance of an optimizedconducting-shell structure with overall diameter 1 mm to the ACresistance of a solid conductor of the same diameter.

FIG. 26 is plot showing the ratio of the resistance of an optimizedconducting-shell structure with overall diameter 1 mm to the DCresistance of the same conductor (21.6 mΩ/m).

FIG. 27 is plot showing the ratio of the resistance of an optimizedconducting-shell structure with overall diameter 1 mm to the resistancewith the same number of elements, but with shells of (optimized) uniformthickness around a copper core.

FIG. 28A and FIG. 28B are diagrams of embodiments of a wireless powerenabled floor tile.

FIG. 29 is a block diagram of an embodiment of a wireless power enabledfloor tile.

FIG. 30 is diagram of a wireless power enables floor system.

FIG. 31 is diagram of a cuttable sheet of resonators.

DETAILED DESCRIPTION

As described above, this disclosure relates to wireless energy transferusing coupled electromagnetic resonators. However, such energy transferis not restricted to electromagnetic resonators, and the wireless energytransfer systems described herein are more general and may beimplemented using a wide variety of resonators and resonant objects.

As those skilled in the art will recognize, important considerations forresonator-based power transfer include resonator efficiency andresonator coupling. Extensive discussion of such issues, e.g., coupledmode theory (CMT), coupling coefficients and factors, quality factors(also referred to as Q-factors), and impedance matching is provided, forexample, in U.S. patent application Ser. No. 12/789,611 published onSep. 23, 2010 as US 20100237709 and entitled “RESONATOR ARRAYS FORWIRELESS ENERGY TRANSFER,” and U.S. patent application Ser. No.12/722,050 published on Jul. 22, 2010 as US 20100181843 and entitled“WIRELESS ENERGY TRANSFER FOR REFRIGERATOR APPLICATION” and incorporatedherein by reference in its entirety as if fully set forth herein.

A resonator may be defined as a resonant structure that can store energyin at least two different forms, and where the stored energy oscillatesbetween the two forms. The resonant structure will have a specificoscillation mode with a resonant (modal) frequency, f, and a resonant(modal) field. The angular resonant frequency, ω, may be defined asω=2πf, the resonant period, T, may be defined as T=1/f=2π/ω, and theresonant wavelength, λ, may be defined as λ=c/f, where c is the speed ofthe associated field waves (light, for electromagnetic resonators). Inthe absence of loss mechanisms, coupling mechanisms or external energysupplying or draining mechanisms, the total amount of energy stored bythe resonator, W, would stay fixed, but the form of the energy wouldoscillate between the two forms supported by the resonator, wherein oneform would be maximum when the other is minimum and vice versa.

For example, a resonator may be constructed such that the two forms ofstored energy are magnetic energy and electric energy. Further, theresonator may be constructed such that the electric energy stored by theelectric field is primarily confined within the structure while themagnetic energy stored by the magnetic field is primarily in the regionsurrounding the resonator. In other words, the total electric andmagnetic energies would be equal, but their localization would bedifferent. Using such structures, energy exchange between at least twostructures may be mediated by the resonant magnetic near-field of the atleast two resonators. These types of resonators may be referred to asmagnetic resonators.

An important parameter of resonators used in wireless power transmissionsystems is the Quality Factor, or Q-factor, or Q, of the resonator,which characterizes the energy decay and is inversely proportional toenergy losses of the resonator. It may be defined as Q=ω*W/P, where P isthe time-averaged power lost at steady state. That is, a resonator witha high-Q has relatively low intrinsic losses and can store energy for arelatively long time. Since the resonator loses energy at its intrinsicdecay rate, 2Γ, its Q, also referred to as its intrinsic Q, is given byQ=ω/2Γ. The quality factor also represents the number of oscillationperiods, T, it takes for the energy in the resonator to decay by afactor of e^(−2π). Note that the quality factor or intrinsic qualityfactor or Q of the resonator is that due only to intrinsic lossmechanisms. The Q of a resonator connected to, or coupled to a powergenerator, g, or load, l, may be called the “loaded quality factor” orthe “loaded Q”. The Q of a resonator in the presence of an extraneousobject that is not intended to be part of the energy transfer system maybe called the “perturbed quality factor” or the “perturbed Q”.

Resonators, coupled through any portion of their near-fields mayinteract and exchange energy. The efficiency of this energy transfer canbe significantly enhanced if the resonators operate at substantially thesame resonant frequency. By way of example, but not limitation, imaginea source resonator with Q_(s) and a device resonator with Q_(d). High-Qwireless energy transfer systems may utilize resonators that are high-Q.The of each resonator may be high. The geometric mean of the resonatorQ's, √{square root over (Q_(s)Q_(d))} may also or instead be high.

The coupling factor, k, is a number between 0≦|k|≦1, and it may beindependent (or nearly independent) of the resonant frequencies of thesource and device resonators when those are placed at sub-wavelengthdistances. Rather the coupling factor k may be determined mostly by therelative geometry and the distance between the source and deviceresonators where the physical decay-law of the field mediating theircoupling is taken into account. The coupling coefficient used in CMT,κ=k√{square root over (ω_(s)ω_(d))}/2, may be a strong function of theresonant frequencies, as well as other properties of the resonatorstructures. In applications for wireless energy transfer utilizing thenear-fields of the resonators, it is desirable to have the size of theresonator be much smaller than the resonant wavelength, so that powerlost by radiation is reduced. In some embodiments, high-Q resonators aresub-wavelength structures. In sonic electromagnetic embodiments, high-Qresonator structures are designed to have resonant frequencies higherthan 100 kHz. In other embodiments, the resonant frequencies may be lessthan 1 GHz.

In exemplary embodiments, the power radiated into the far-field by thesesub wavelength resonators may be further reduced by lowering theresonant frequency of the resonators and the operating frequency of thesystem. In other embodiments, the far field radiation may be reduced byarranging for the far fields of two or more resonators to interferedestructively in the far field.

In a wireless energy transfer system a resonator may be used as awireless energy source, a wireless energy capture device, a repeater ora combination thereof. In embodiments a resonator may alternate betweentransferring energy, receiving energy or relaying energy. In a wirelessenergy transfer system one or more magnetic resonators may be coupled toan energy source and be energized to produce an oscillating magneticnear-field. Other resonators that are within the oscillating magneticnear-fields may capture these fields and convert the energy intoelectrical energy that may be used to power or charge a load therebyenabling wireless transfer of useful energy.

The so-called “useful” energy in a useful energy exchange is the energyor power that must be delivered to a device in order to power or chargeit at an acceptable rate. The transfer efficiency that corresponds to auseful energy exchange may be system or application-dependent. Forexample, high power vehicle charging applications that transferkilowatts of power may need to be at least 80% efficient in order tosupply useful amounts of power resulting in a useful energy exchangesufficient to recharge a vehicle battery without significantly heatingup various components of the transfer system. In some consumerelectronics applications, a useful energy exchange may include anyenergy transfer efficiencies greater than 10%, or any other amountacceptable to keep rechargeable batteries “topped off” and running forlong periods of time. In implanted medical device applications, a usefulenergy exchange may be any exchange that does not harm the patient butthat extends the life of a battery or wakes up a sensor or monitor orstimulator. In such applications, 100 mW of power or less may be useful.In distributed sensing applications, power transfer of microwatts may beuseful, and transfer efficiencies may be well below 1%.

A useful energy exchange for wireless energy transfer in a powering orrecharging application may be efficient, highly efficient, or efficientenough, as long as the wasted energy levels, heat dissipation, andassociated field strengths are within tolerable limits and are balancedappropriately with related factors such as cost, weight, size, and thelike.

The resonators may be referred to as source resonators, deviceresonators, first resonators, second resonators, repeater resonators,and the like. Implementations may include three (3) or more resonators.For example, a single source resonator may transfer energy to multipledevice resonators or multiple devices. Energy may be transferred from afirst device to a second, and then from the second device to the third,and so forth. Multiple sources may transfer energy to a single device orto multiple devices connected to a single device resonator or tomultiple devices connected to multiple device resonators. Resonators mayserve alternately or simultaneously as sources, devices, and/or they maybe used to relay power from a source in one location to a device inanother location. Intermediate electromagnetic resonators may be used toextend the distance range of wireless energy transfer systems and/or togenerate areas of concentrated magnetic near-fields. Multiple resonatorsmay be daisy-chained together, exchanging energy over extended distancesand with a wide range of sources and devices. For example, a sourceresonator may transfer power to a device resonator via several repeaterresonators. Energy from a source may be transferred to a first repeaterresonator, the first repeater resonator may transfer the power to asecond repeater resonator and the second to a third and so on until thefinal repeater resonator transfers its energy to a device resonator. Inthis respect the range or distance of wireless energy transfer may beextended and/or tailored by adding repeater resonators. High powerlevels may be split between multiple sources, transferred to multipledevices and recombined at a distant location.

The resonators may be designed using coupled mode theory models, circuitmodels, electromagnetic field models, and the like. The resonators maybe designed to have tunable characteristic sizes. The resonators may bedesigned to handle different power levels. In exemplary embodiments,high power resonators may require larger conductors and higher currentor voltage rated components than lower power resonators.

FIG. 1 shows a diagram of exemplary configurations and arrangements of awireless energy transfer system. A wireless energy transfer system mayinclude at least one source resonator (R1) 104 (optionally R6, 112)coupled to an energy source 102 and optionally a sensor and control unit108. The energy source may be a source of any type of energy capable ofbeing converted into electrical energy that may be used to drive thesource resonator 104. The energy source may be a battery, a solar panel,the electrical mains, a wind or water turbine, an electromagneticresonator, a generator, and the like. The electrical energy used todrive the magnetic resonator is converted into oscillating magneticfields by the resonator. The oscillating magnetic fields may be capturedby other resonators which may be device resonators (R2) 106, (R3) 116that are optionally coupled to an energy drain 110. The oscillatingfields may be optionally coupled to repeater resonators (R4, R5) thatare configured to extend or tailor the wireless energy transfer region.Device resonators may capture the magnetic fields in the vicinity ofsource resonator(s), repeater resonators and other device resonators andconvert them into electrical energy that may be used by an energy drain.The energy drain 110 may be an electrical, electronic, mechanical orchemical device and the like configured to receive electrical energy.Repeater resonators may capture magnetic fields in the vicinity ofsource, device and repeater resonator(s) and may pass the energy on toother resonators.

A wireless energy transfer system may comprise a single source resonator104 coupled to an energy source 102 and a single device resonator 106coupled to an energy drain 110. In embodiments a wireless energytransfer system may comprise multiple source resonators coupled to oneor more energy sources and may comprise multiple device resonatorscoupled to one or more energy drains.

In embodiments the energy may be transferred directly between a sourceresonator 104 and a device resonator 106. In other embodiments theenergy may be transferred from one or more source resonators 104, 112 toone or more device resonators 106, 116 via any number of intermediateresonators which may be device resonators, source resonators, repeaterresonators, and the like. Energy may be transferred via a network orarrangement of resonators 114 that may include subnetworks 118, 120arranged in any combination of topologies such as token ring, mesh, adhoc, and the like.

In embodiments the wireless energy transfer system may comprise acentralized sensing and control system 108. In embodiments parameters ofthe resonators, energy sources, energy drains, network topologies,operating parameters, etc. may be monitored and adjusted from a controlprocessor to meet specific operating parameters of the system. A centralcontrol processor may adjust parameters of individual components of thesystem to optimize global energy transfer efficiency, to optimize theamount of power transferred, and the like. Other embodiments may bedesigned to have a substantially distributed sensing and control system.Sensing and control may be incorporated into each resonator or group ofresonators, energy sources, energy drains, and the like and may beconfigured to adjust the parameters of the individual components in thegroup to maximize or minimize the power delivered, to maximize energytransfer efficiency in that group and the like.

In embodiments, components of the wireless energy transfer system mayhave wireless or wired data communication links to other components suchas devices, sources, repeaters, power sources, resonators, and the likeand may transmit or receive data that can be used to enable thedistributed or centralized sensing and control. A wireless communicationchannel may be separate from the wireless energy transfer channel, or itmay be the same. In one embodiment the resonators used for powerexchange may also be used to exchange information. In some cases,information may be exchanged by modulating a component in a source ordevice circuit and sensing that change with port parameter or othermonitoring equipment. Resonators may signal each other by tuning,changing, varying, dithering, and the like, the resonator parameterssuch as the impedance of the resonators which may affect the reflectedimpedance of other resonators in the system. The systems and methodsdescribed herein may enable the simultaneous transmission of power andcommunication signals between resonators in wireless power transmissionsystems, or it may enable the transmission of power and communicationsignals during different time periods or at different frequencies usingthe same magnetic fields that are used during the wireless energytransfer. In other embodiments wireless communication may be enabledwith a separate wireless communication channel such as WiFi, Bluetooth,Infrared, NFC, and the like.

In embodiments, a wireless energy transfer system may include multipleresonators and overall system performance may be improved by control ofvarious elements in the system. For example, devices with lower powerrequirements may tune their resonant frequency away from the resonantfrequency of a high-power source that supplies power to devices withhigher power requirements. For another example, devices needing lesspower may adjust their rectifier circuits so that they draw less powerfrom the source. In these ways, low and high power devices may safelyoperate or charge from a single high power source. In addition, multipledevices in a charging zone may find the power available to themregulated according to any of a variety of consumption controlalgorithms such as First-Come-First-Serve, Best Effort, GuaranteedPower, etc. The power consumption algorithms may be hierarchical innature, giving priority to certain users or types of devices, or it maysupport any number of users by equally sharing the power that isavailable in the source. Power may be shared by any of the multiplexingtechniques described in this disclosure.

In embodiments electromagnetic resonators may be realized or implementedusing a combination of shapes, structures, and configurations.Electromagnetic resonators may include an inductive element, adistributed inductance, or a combination of inductances with a totalinductance, L, and a capacitive element, a distributed capacitance, or acombination of capacitances, with a total capacitance, C. A minimalcircuit model of an electromagnetic resonator comprising capacitance,inductance and resistance, is shown in FIG. 2F. The resonator mayinclude an inductive element 238 and a capacitive element 240. Providedwith initial energy, such as electric field energy stored in thecapacitor 240, the system will oscillate as the capacitor dischargestransferring energy into magnetic field energy stored in the inductor238 which in turn transfers energy back into electric field energystored in the capacitor 240. Intrinsic losses in these electromagneticresonators include losses due to resistance in the inductive andcapacitive elements and to radiation losses, and are represented by theresistor, R, 242 in FIG. 2F.

FIG. 2A shows a simplified drawing of an exemplary magnetic resonatorstructure. The magnetic resonator may include a loop of conductor actingas an inductive element 202 and a capacitive element 204 at the ends ofthe conductor loop. The inductor 202 and capacitor 204 of anelectromagnetic resonator may be bulk circuit elements, or theinductance and capacitance may be distributed and may result from theway the conductors are formed, shaped, or positioned, in the structure.

For example, the inductor 202 may be realized by shaping a conductor toenclose a surface area, as shown in FIG. 2A. This type of resonator maybe referred to as a capacitively-loaded loop inductor. Note that we mayuse the terms “loop” or “coil” to indicate generally a conductingstructure (wire, tube, strip, etc), enclosing a surface of any shape anddimension, with any number of turns. In FIG. 2A, the enclosed surfacearea is circular, but the surface may be any of a wide variety of othershapes and sizes and may be designed to achieve certain systemperformance specifications. In embodiments the inductance may berealized using inductor elements, distributed inductance, networks,arrays, series and parallel combinations of inductors and inductances,and the like. The inductance may be fixed or variable and may be used tovary impedance matching as well as resonant frequency operatingconditions.

There are a variety of ways to realize the capacitance required toachieve the desired resonant frequency for a resonator structure.Capacitor plates 204 may be formed and utilized as shown in FIG. 2A, orthe capacitance may be distributed and be realized between adjacentwindings of a multi-loop conductor. The capacitance may be realizedusing capacitor elements, distributed capacitance, networks, arrays,series and parallel combinations of capacitances, and the like. Thecapacitance may be fixed or variable and may be used to vary impedancematching as well as resonant frequency operating conditions.

The inductive elements used in magnetic resonators may contain more thanone loop and may spiral inward or outward or up or down or in somecombination of directions. In general, the magnetic resonators may havea variety of shapes, sizes and number of turns and they may be composedof a variety of conducing materials. The conductor 210, for example, maybe a wire, a Litz wire, a ribbon, a pipe, a trace formed from conductingink, paint, gels, and the like or from single or multiple traces printedon a circuit board. An exemplary embodiment of a trace pattern on asubstrate 208 forming inductive loops is depicted in FIG. 2B.

In embodiments the inductive elements may be formed using magneticmaterials of any size, shape thickness, and the like, and of materialswith a wide range of permeability and loss values. These magneticmaterials may be solid blocks, they may enclose hollow volumes, they maybe formed from many smaller pieces of magnetic material tiled and orstacked together, and they may be integrated with conducting sheets orenclosures made from highly conducting materials. Conductors may bewrapped around the magnetic materials to generate the magnetic field.These conductors may be wrapped around one or more than one axis of thestructure. Multiple conductors may be wrapped around the magneticmaterials and combined in parallel, or in series, or via a switch toform customized near-field patterns and/or to orient the dipole momentof the structure. Examples of resonators comprising magnetic materialare depicted in FIGS. 2C, 2D, 2E. In FIG. 2D the resonator comprisesloops of conductor 224 wrapped around a core of magnetic material 222creating a structure that has a magnetic dipole moment 228 that isparallel to the axis of the loops of the conductor 224. The resonatormay comprise multiple loops of conductor 216, 212 wrapped in orthogonaldirections around the magnetic material 214 forming a resonator with amagnetic dipole moment 218, 220 that may be oriented in more than onedirection as depicted in FIG. 2C, depending on how the conductors aredriven.

An electromagnetic resonator may have a characteristic, natural, orresonant frequency determined by its physical properties. This resonantfrequency is the frequency at which the energy stored by the resonatoroscillates between that stored by the electric field, W_(E),(W_(E)=q²/2C, where q is the charge on the capacitor, C) and that storedby the magnetic field, W_(B), (W_(B)=Li²/2, where i is the currentthrough the inductor, L) of the resonator. The frequency at which thisenergy is exchanged may be called the characteristic frequency, thenatural frequency, or the resonant frequency of the resonator, and isgiven by ω,

$\omega = {{2\pi \; f} = {\sqrt{\frac{1}{LC}}.}}$

The resonant frequency of the resonator may be changed by tuning theinductance, L, and/or the capacitance, C, of the resonator. In oneembodiment system parameters are dynamically adjustable or tunable toachieve as close as possible to optimal operating conditions. However,based on the discussion above, efficient enough energy exchange may berealized even if some system parameters are not variable or componentsare not capable of dynamic adjustment.

In embodiments a resonator may comprise an inductive element coupled tomore than one capacitor arranged in a network of capacitors and circuitelements. In embodiments the coupled network of capacitors and circuitelements may be used to define more than one resonant frequency of theresonator. In embodiments a resonator may be resonant, or partiallyresonant, at more than one frequency.

In embodiments, a wireless power source may comprise of at least oneresonator coil coupled to a power supply, which may be a switchingamplifier, such as a class-D amplifier or a class-E amplifier or acombination thereof. In this case, the resonator coil is effectively apower load to the power supply. In embodiments, a wireless power devicemay comprise of at least one resonator coil coupled to a power load,which may be a switching rectifier, such as a class-D rectifier or aclass-E rectifier or a combination thereof. In this case, the resonatorcoil is effectively a power supply for the power load, and the impedanceof the load directly relates also to the work-drainage rate of the loadfrom the resonator coil. The efficiency of power transmission between apower supply and a power load may be impacted by how closely matched theoutput impedance of the power source is to the input impedance of theload. Power may be delivered to the load at a maximum possibleefficiency, when the input impedance of the load is equal to the complexconjugate of the internal impedance of the power supply. Designing thepower supply or power load impedance to obtain a maximum powertransmission efficiency is often called “impedance matching”, and mayalso referred to as optimizing the ratio of useful-to-lost powers in thesystem. Impedance matching may be performed by adding networks or setsof elements such as capacitors, inductors, transformers, switches,resistors, an the like, to form impedance matching networks between apower supply and a power load. In embodiments, mechanical adjustmentsand changes in element positioning may be used to achieve impedancematching. For varying loads, the impedance matching network may includevariable components that are dynamically adjusted to ensure that theimpedance at the power supply terminals looking towards the load and thecharacteristic impedance of the power supply remain substantiallycomplex conjugates of each other, even in dynamic environments andoperating scenarios.

In embodiments, impedance matching may be accomplished by tuning theduty cycle, and/or the phase, and/or the frequency of the driving signalof the power supply or by tuning a physical component within the powersupply, such as a capacitor. Such a tuning mechanism may be advantageousbecause it may allow impedance matching between a power supply and aload without the use of a tunable impedance matching network, or with asimplified tunable impedance matching network, such as one that hasfewer tunable components for example. In embodiments, tuning the dutycycle, and/or frequency, and/or phase of the driving signal to a powersupply may yield a dynamic impedance matching system with an extendedtuning range or precision, with higher power, voltage and/or currentcapabilities, with faster electronic control, with fewer externalcomponents, and the like.

In some wireless energy transfer systems the parameters of the resonatorsuch as the inductance may be affected by environmental conditions suchas surrounding objects, temperature, orientation, number and position ofother resonators and the like. Changes in operating parameters of theresonators may change certain system parameters, such as the efficiencyof transferred power in the wireless energy transfer. For example,high-conductivity materials located near a resonator may shift theresonant frequency of a resonator and detune it from other resonantobjects. In some embodiments, a resonator feedback mechanism is employedthat corrects its frequency by changing a reactive element (e.g., aninductive element or capacitive element). In order to achieve acceptablematching conditions, at least some of the system parameters may need tobe dynamically adjustable or tunable. All the system parameters may bedynamically adjustable or tunable to achieve approximately the optimaloperating conditions. However, efficient enough energy exchange may berealized even if all or some system parameters are not variable. In someexamples, at least some of the devices may not be dynamically adjusted.In some examples, at least some of the sources may not be dynamicallyadjusted. In some examples, at least some of the intermediate resonatorsmay not be dynamically adjusted. In some examples, none of the systemparameters may be dynamically adjusted.

In some embodiments changes in parameters of components may be mitigatedby selecting components with characteristics that change in acomplimentary or opposite way or direction when subjected to differencesin operating environment or operating point. In embodiments, a systemmay be designed with components, such as capacitors, that have anopposite dependence or parameter fluctuation due to temperature, powerlevels, frequency, and the like. In some embodiments, the componentvalues as a function of temperature may be stored in a look-up table ina system microcontroller and the reading from a temperature sensor maybe used in the system control feedback loop to adjust other parametersto compensate for the temperature induced component value changes.

In some embodiments the changes in parameter values of components may becompensated with active tuning circuits comprising tunable components.Circuits that monitor the operating environment and operating point ofcomponents and system may be integrated in the design. The monitoringcircuits may provide the signals necessary to actively compensate forchanges in parameters of components. For example, a temperature readingmay be used to calculate expected changes in, or to indicate previouslymeasured values of, capacitance of the system allowing compensation byswitching in other capacitors or tuning capacitors to maintain thedesired capacitance over a range of temperatures. In embodiments, the RFamplifier switching waveforms may be adjusted to compensate forcomponent value or load changes in the system. In some embodiments thechanges in parameters of components may be compensated with activecooling, heating, active environment conditioning, and the like.

The parameter measurement circuitry may measure or monitor certainpower, voltage, and current, signals in the system, and processors orcontrol circuits may adjust certain settings or operating parametersbased on those measurements. In addition the magnitude and phase ofvoltage and current signals, and the magnitude of the power signals,throughout the system may be accessed to measure or monitor the systemperformance. The measured signals referred to throughout this disclosuremay be any combination of port parameter signals, as well as voltagesignals, current signals, power signals, temperatures signals and thelike. These parameters may be measured using analog or digitaltechniques, they may be sampled and processed, and they may be digitizedor converted using a number of known analog and digital processingtechniques. In embodiments, preset values of certain measured quantitiesare loaded in a system controller or memory location and used in variousfeedback and control loops, in embodiments, any combination of measured,monitored, and/or preset signals may be used in feedback circuits orsystems to control the operation of the resonators and/or the system.

Adjustment algorithms may be used to adjust the frequency, Q, and/orimpedance of the magnetic resonators. The algorithms may take as inputsreference signals related to the degree of deviation from a desiredoperating point for the system and may output correction or controlsignals related to that deviation that control variable or tunableelements of the system to bring the system back towards the desiredoperating point or points. The reference signals for the magneticresonators may be acquired while the resonators are exchanging power ina wireless power transmission system, or they may be switched out of thecircuit during system operation. Corrections to the system may beapplied or performed continuously, periodically, upon a thresholdcrossing, digitally, using analog methods, and the like.

In embodiments, lossy extraneous materials and objects may introducepotential reductions in efficiencies by absorbing the magnetic and/orelectric energy of the resonators of the wireless power transmissionsystem. Those impacts may be mitigated in various embodiments bypositioning resonators to minimize the effects of the lossy extraneousmaterials and objects and by placing structural field shaping elements(e.g., conductive structures, plates and sheets, magnetic materialstructures, plates and sheets, and combinations thereof) to minimizetheir effect.

One way to reduce the impact of lossy materials on a resonator is to usehigh-conductivity materials, magnetic materials, or combinations thereofto shape the resonator fields such that they avoid the lossy objects. Inan exemplary embodiment, a layered structure of high-conductivitymaterial and magnetic material may tailor, shape, direct, reorient, etc.the resonator's electromagnetic fields so that they avoid lossy objectsin their vicinity by deflecting the fields. FIG. 2D shows a top view ofa resonator with a sheet of conductor 226 below the magnetic materialthat may used to tailor the fields of the resonator so that they avoidlossy objects that may be below the sheet of conductor 226. The layer orsheet of good 226 conductor may comprise any high conductivity materialssuch as copper, silver, aluminum, as may be most appropriate for a givenapplication. In certain embodiments, the layer or sheet of goodconductor is thicker than the skin depth of the conductor at theresonator operating frequency. The conductor sheet may be preferablylarger than the size of the resonator, extending beyond the physicalextent of the resonator.

In environments and systems where the amount of power being transmittedcould present a safety hazard to a person or animal that may intrudeinto the active field volume, safety measures may be included in thesystem. In embodiments where power levels require particularized safetymeasures, the packaging, structure, materials, and the like of theresonators may be designed to provide a spacing or “keep away” zone fromthe conducting loops in the magnetic resonator. To provide furtherprotection, high-Q resonators and power and control circuitry may belocated in enclosures that confine high voltages or currents to withinthe enclosure, that protect the resonators and electrical componentsfrom weather, moisture, sand, dust, and other external elements, as wellas from impacts, vibrations, scrapes, explosions, and other types ofmechanical shock. Such enclosures call for attention to various factorssuch as thermal dissipation to maintain an acceptable operatingtemperature range for the electrical components and the resonator. Inembodiments, enclosure may be constructed of non-lossy materials such ascomposites, plastics, wood, concrete, and the like and may be used toprovide a minimum distance from lossy objects to the resonatorcomponents. A minimum separation distance from lossy objects orenvironments which may include metal objects, salt water, oil and thelike, may improve the efficiency of wireless energy transfer. Inembodiments, a “keep away” zone may be used to increase the perturbed Qof a resonator or system of resonators. In embodiments a minimumseparation distance may provide for a more reliable or more constantoperating parameters of the resonators.

In embodiments, resonators and their respective sensor and controlcircuitry may have various levels of integration with other electronicand control systems and subsystems. In some embodiments the power andcontrol circuitry and the device resonators are completely separatemodules or enclosures with minimal integration to existing systems,providing a power output and a control and diagnostics interface. Insome embodiments a device is configured to house a resonator and circuitassembly in a cavity inside the enclosure, or integrated into thehousing or enclosure of the device.

Example Resonator Circuitry

FIGS. 3 and 4 show high level block diagrams depicting power generation,monitoring, and control components for exemplary sources of a wirelessenergy transfer system. FIG. 3 is a block diagram of a source comprisinga half-bridge switching power amplifier and some of the associatedmeasurement, tuning, and control circuitry. FIG. 4 is a block diagram ofa source comprising a full-bridge switching amplifier and some of theassociated measurement, tuning, and control circuitry.

The half bridge system topology depicted in FIG. 3 may comprise aprocessing unit that executes a control algorithm 328. The processingunit executing a control algorithm 328 may be a microcontroller, anapplication specific circuit, a field programmable gate array, aprocessor, a digital signal processor, and the like. The processing unitmay be a single device or it may be a network of devices. The controlalgorithm may run on any portion of the processing unit. The algorithmmay be customized for certain applications and may comprise acombination of analog and digital circuits and signals. The masteralgorithm may measure and adjust voltage signals and levels, currentsignals and levels, signal phases, digital count settings, and the like.

The system may comprise an optional source/device and/or source/otherresonator communication controller 332 coupled to wireless communicationcircuitry 312. The optional source/device and/or source/other resonatorcommunication controller 332 may be part of the same processing unitthat executes the master control algorithm, it may a part or a circuitwithin a microcontroller 302, it may be external to the wireless powertransmission modules, it may be substantially similar to communicationcontrollers used in wire powered or battery powered applications butadapted to include some new or different functionality to enhance orsupport wireless power transmission.

The system may comprise a PWM generator 306 coupled to at least twotransistor gate drivers 334 and may be controlled by the controlalgorithm. The two transistor gate drivers 334 may be coupled directlyor via gate drive transformers to two power transistors 336 that drivethe source resonator coil 344 through impedance matching networkcomponents 342. The power transistors 336 may be coupled and poweredwith an adjustable DC supply 304 and the adjustable DC supply 304 may becontrolled by a variable bus voltage, Vbus. The Vbus controller may becontrolled by the control algorithm 328 and may be part of or integratedinto, a microcontroller 302 or other integrated circuits. The Vbuscontroller 326 may control the voltage output of an adjustable DC supply304 which may be used to control power output of the amplifier and powerdelivered to the resonator coil 344.

The system may comprise sensing and measurement circuitry includingsignal filtering and buffering circuits 318, 320 that may shape, modify,filter, process, buffer, and the like, signals prior to their input toprocessors and/or converters such as analog to digital converters (ADC)314, 316, for example. The processors and converters such as ADCs 314,316 may be integrated into a microcontroller 302 or may be separatecircuits that may be coupled to a processing core 330. Based on measuredsignals, the control algorithm 328 may generate, limit, initiate,extinguish, control, adjust, or modify the operation of any of the PWMgenerator 306, the communication controller 332, the Vbus control 326,the source impedance matching controller 338, the filter/bufferingelements, 318, 320, the converters, 314, 316, the resonator coil 344,and may be part of, or integrated into, a microcontroller 302 or aseparate circuit. The impedance matching networks 342 and resonatorcoils 344 may include electrically controllable, variable, or tunablecomponents such as capacitors, switches, inductors, and the like, asdescribed herein, and these components may have their component valuesor operating points adjusted according to signals received from thesource impedance matching controller 338. Components may be tuned toadjust the operation and characteristics of the resonator including thepower delivered to and by the resonator, the resonant frequency of theresonator, the impedance of the resonator, the Q of the resonator, andany other coupled systems, and the like. The resonator may be any typeor structure resonator described herein including a capacitively loadedloop resonator, a planer resonator comprising a magnetic material or anycombination thereof.

The full bridge system topology depicted in FIG. 4 may comprise aprocessing unit that executes a master control algorithm 328. Theprocessing unit executing the control algorithm 328 may be amicrocontroller, an application specific circuit, a field programmablegate array, a processor, a digital signal processor, and the like. Thesystem may comprise a source/device and/or source/other resonatorcommunication controller 332 coupled to wireless communication circuitry312. The source/device and/or source/other resonator communicationcontroller 332 may be part of the same processing unit that executesthat master control algorithm, it may a part or a circuit within amicrocontroller 302, it may be external to the wireless powertransmission modules, it may be substantially similar to communicationcontrollers used in wire powered or battery powered applications butadapted to include some new or different functionality to enhance orsupport wireless power transmission.

The system may comprise a PWM generator 410 with at least two outputscoupled to at least four transistor gate drivers 334 that may becontrolled by signals generated in a master control algorithm. The fourtransistor gate drivers 334 may be coupled to four power transistors 336directly or via gate drive transformers that may drive the sourceresonator coil 344 through impedance matching networks 342. The powertransistors 336 may be coupled and powered with an adjustable DC supply304 and the adjustable DC supply 304 may be controlled by a Vbuscontroller 326 which may be controlled by a master control algorithm.The Vbus controller 326 may control the voltage output of the adjustableDC supply 304 which may be used to control power output of the amplifierand power delivered to the resonator coil 344.

The system may comprise sensing and measurement circuitry includingsignal filtering and buffering circuits 318, 320 and differential/singleended conversion circuitry 402, 404 that may shape, modify, filter,process, buffer, and the like, signals prior to being input toprocessors and/or converters such as analog to digital converters (ADC)314, 316. The processors and/or converters such as ADC 314, 316 may beintegrated into a microcontroller 302 or may be separate circuits thatmay be coupled to a processing core 330. Based on measured signals, themaster control algorithm may generate, limit, initiate, extinguish,control, adjust, or modify the operation of any of the PWM generator410, the communication controller 332, the Vbus controller 326, thesource impedance matching controller 338, the filter/buffering elements,318, 320, differential/single ended conversion circuitry 402, 404, theconverters, 314, 316, the resonator coil 344, and may be part of orintegrated into a microcontroller 302 or a separate circuit.

Impedance matching networks 342 and resonator coils 344 may compriseelectrically controllable, variable, or tunable components such ascapacitors, switches, inductors, and the like, as described herein, andthese components may have their component values or operating pointsadjusted according to signals received from the source impedancematching controller 338. Components may be tuned to enable tuning of theoperation and characteristics of the resonator including the powerdelivered to and by the resonator, the resonant frequency of theresonator, the impedance of the resonator, the Q of the resonator, andany other coupled systems, and the like. The resonator may be any typeor structure resonator described herein including a capacitively loadedloop resonator, a planar resonator comprising a magnetic material or anycombination thereof.

Impedance matching networks may comprise fixed value components such ascapacitors, inductors, and networks of components as described herein.Parts of the impedance matching networks, A, B and C, may compriseinductors, capacitors, transformers, and series and parallelcombinations of such components, as described herein. In someembodiments, parts of the impedance matching networks A, B, and C, maybe empty (short-circuited). In some embodiments, part B comprises aseries combination of an inductor and a capacitor, and part C is empty.

The full bridge topology may allow operation at higher output powerlevels using the same DC bus voltage as an equivalent half bridgeamplifier. The half bridge exemplary topology of FIG. 3 may provide asingle-ended drive signal, while the exemplary full bridge topology ofFIG. 4 may provide a differential drive to the source resonator 308. Theimpedance matching topologies and components and the resonator structuremay be different for the two systems, as discussed herein.

The exemplary systems depicted in FIGS. 3 and 4 may further includefault detection circuitry 340 that may be used to trigger the shutdownof the microcontroller in the source amplifier or to change or interruptthe operation of the amplifier. This protection circuitry may comprise ahigh speed comparator or comparators to monitor the amplifier returncurrent, the amplifier bus voltage (Vbus) from the DC supply 304, thevoltage across the source resonator 308 and/or the optional tuningboard, or any other voltage or current signals that may cause damage tocomponents in the system or may yield undesirable operating conditions.Preferred embodiments may depend on the potentially undesirableoperating modes associated with different applications. In someembodiments, protection circuitry may not be implemented or circuits maynot be populated. In some embodiments, system and component protectionmay be implemented as part of a master control algorithm and othersystem monitoring and control circuits. In embodiments, dedicated faultcircuitry 340 may include an output (not shown) coupled to a mastercontrol algorithm 328 that may trigger a system shutdown, a reduction ofthe output power (e.g. reduction of Vbus), a change to the PWMgenerator, a change in the operating frequency, a change to a tuningelement, or any other reasonable action that may be implemented by thecontrol algorithm 328 to adjust the operating point mode, improve systemperformance, and/or provide protection.

As described herein, sources in wireless power transfer systems may usea measurement of the input impedance of the impedance matching network342 driving source resonator coil 344 as an error or control signal fora system control loop that may be part of the master control algorithm.In exemplary embodiments, variations in any combination of threeparameters may be used to tune the wireless power source to compensatefor changes in environmental conditions, for changes in coupling, forchanges in device power demand, for changes in module, circuit,component or subsystem performance, for an increase or decrease in thenumber or sources, devices, or repeaters in the system, for userinitiated changes, and the like. In exemplary embodiments, changes tothe amplifier duty cycle, to the component values of the variableelectrical components such as variable capacitors and inductors, and tothe DC bus voltage may be used to change the operating point oroperating range of the wireless source and improve some system operatingvalue. The specifics of the control algorithms employed for differentapplications may vary depending on the desired system performance andbehavior.

Impedance measurement circuitry such as described herein, and shown inFIGS. 3 and 4, may be implemented using two-channel simultaneoussampling ADCs and these ADCs may be integrated into a microcontrollerchip or may be part of a separate circuit. Simultaneously sampling ofthe voltage and current signals at the input to a source resonator'simpedance matching network and/or the source resonator, may yield thephase and magnitude information of the current and voltage signals andmay be processed using known signal processing techniques to yieldcomplex impedance parameters. In some embodiments, monitoring only thevoltage signals or only the current signals may be sufficient.

The impedance measurements described herein may use direct samplingmethods which may be relatively simpler than some other known samplingmethods. In embodiments, measured voltage and current signals may beconditioned, filtered and scaled by filtering/buffering circuitry beforebeing input to ADCs. In embodiments, the filter/buffering circuitry maybe adjustable to work at a variety of signal levels and frequencies, andcircuit parameters such as filter shapes and widths may be adjustedmanually, electronically, automatically, in response to a controlsignal, by the master control algorithm, and the like. Exemplaryembodiments of fitter/buffering circuits are shown in FIGS. 3, 4, and 5.

FIG. 5 shows more detailed views of exemplary circuit components thatmay be used in filter/buffering circuitry. In embodiments, and dependingon the types of ADCs used in the system designs, single-ended amplifiertopologies may reduce the complexity of the analog signal measurementpaths used to characterize system, subsystem, module and/or componentperformance by eliminating the need for hardware to convert fromdifferential to single-ended signal formats. In other implementations,differential signal formats may be preferable. The implementations shownin FIG. 5 are exemplary, and should not be construed to be the onlypossible way to implement the functionality described herein. Rather itshould be understood that the analog signal path may employ componentswith different input requirements and hence may have different signalpath architectures.

In both the single ended and differential amplifier topologies, theinput current to the impedance matching networks 342 driving theresonator coils 344 may be obtained by measuring the voltage across acapacitor 324, or via a current sensor of some type. For the exemplarysingle-ended amplifier topology in FIG. 3, the current may be sensed onthe ground return path from the impedance matching network 342. For theexemplary differential power amplifier depicted in FIG. 4, the inputcurrent to the impedance matching networks 342 driving the resonatorcoils 344 may be measured using a differential amplifier across theterminals of a capacitor 324 or via a current sensor of some type. Inthe differential topology of FIG. 4, the capacitor 324 may be duplicatedat the negative output terminal of the source power amplifier.

In both topologies, after single ended signals representing the inputvoltage and current to the source resonator and impedance matchingnetwork are obtained, the signals may be filtered 502 to obtain thedesired portions of the signal waveforms. In embodiments, the signalsmay be filtered to obtain the fundamental component of the signals. Inembodiments, the type of filtering performed, such as low pass,bandpass, notch, and the like, as well as the filter topology used, suchas elliptical, Chebyshev, Butterworth, and the like, may depend on thespecific requirements of the system. In some embodiments, no filteringwill be required.

The voltage and current signals may be amplified by an optionalamplifier 504. The gain of the optional amplifier 504 may be fixed orvariable. The gain of the amplifier may be controlled manually,electronically, automatically, in response to a control signal, and thelike. The gain of the amplifier may be adjusted in a feedback loop, inresponse to a control algorithm, by the master control algorithm, andthe like. In embodiments, required performance specifications for theamplifier may depend on signal strength and desired measurementaccuracy, and may be different for different application scenarios andcontrol algorithms.

The measured analog signals may have a DC offset added to them, 506,which may be required to bring the signals into the input voltage rangeof the ADC which for some systems may be 0 to 3.3V. In some systems thisstage may not be required, depending on the specifications of theparticular ADC used.

As described above, the efficiency of power transmission between a powergenerator and a power load may be impacted by how closely matched theoutput impedance of the generator is to the input impedance of the load.In an exemplary system as shown in FIG. 6A, power may be delivered tothe load at a maximum possible efficiency, when the input impedance ofthe load 604 is equal to the complex conjugate of the internal impedanceof the power generator or the power amplifier 602. Designing thegenerator or load impedance to obtain a high and/or maximum powertransmission efficiency may be called “impedance matching”. Impedancematching may be performed by inserting appropriate networks or sets ofelements such as capacitors, resistors, inductors, transformers,switches and the like, to form an impedance matching network 606,between a power generator 602 and a power load 604 as shown in FIG. 6B.In other embodiments, mechanical adjustments and changes in elementpositioning may be used to achieve impedance matching. As describedabove for varying loads, the impedance matching network 606 may includevariable components that are dynamically adjusted to ensure that theimpedance at the generator terminals looking towards the load and thecharacteristic impedance of the generator remain substantially complexconjugates of each other, even in dynamic environments and operatingscenarios. In embodiments, dynamic impedance matching may beaccomplished by tuning the duty cycle, and/or the phase, and/or thefrequency of the driving signal of the power generator or by tuning aphysical component within the power generator, such as a capacitor, asdepicted in FIG. 6C. Such a tuning mechanism may be advantageous becauseit may allow impedance matching between a power generator 608 and a loadwithout the use of a tunable impedance matching network, or with asimplified tunable impedance matching network 606, such as one that hasfewer tunable components for example. In embodiments, tuning the dutycycle, and/or frequency, and/or phase of the driving signal to a powergenerator may yield a dynamic impedance matching system with an extendedtuning range or precision, with higher power, voltage and/or currentcapabilities, with faster electronic control, with fewer externalcomponents, and the like. The impedance matching methods, architectures,algorithms, protocols, circuits, measurements, controls, and the like,described below, may be useful in systems where power generators drivehigh-Q magnetic resonators and in high-Q wireless power transmissionsystems as described herein. In wireless power transfer systems a powergenerator may be a power amplifier driving a resonator, sometimesreferred to as a source resonator, which may be a load to the poweramplifier. In wireless power applications, it may be preferable tocontrol the impedance matching between a power amplifier and a resonatorload to control the efficiency of the power delivery from the poweramplifier to the resonator. The impedance matching may be accomplished,or accomplished in part, by tuning or adjusting the duty cycle, and/orthe phase, and/or the frequency of the driving signal of the poweramplifier that drives the resonator.

Efficiency of Switching Amplifiers

Switching amplifiers, such as class D, E, F amplifiers, and the like orany combinations thereof, deliver power to a load at a maximumefficiency when almost no power is dissipated on the switching elementsof the amplifier. This operating condition may be accomplished bydesigning the system so that the switching operations which are mostcritical (namely those that are most likely to lead to switching losses)are done when either or both of the voltage across the switching elementand the current through the switching element are nearly zero. Theseconditions may be referred to as Zero Voltage Switching (ZVS) and ZeroCurrent Switching (ZCS) conditions respectively. When an amplifieroperates at ZVS and/or ZCS either the voltage across the switchingelement or the current through the switching element is zero and thus nopower can be dissipated in the switch. Since a switching amplifier mayconvert DC (or very low frequency AC) power to AC power at a specificfrequency or range of frequencies, a filter may be introduced before theload to prevent unwanted harmonics that may be generated by theswitching process from reaching the load and being dissipated there. Inembodiments, a switching amplifier may be designed to operate at maximumefficiency of power conversion, when connected to a resonant load, witha quality factor (say Q>5), and of a specific impedanceZ*_(O)=R_(O)+jX_(O), which leads to simultaneous ZVS and ZCS. We defineZ_(O)=R_(O)−jX_(O) as the characteristic impedance of the amplifier, sothat achieving maximum power transmission efficiency is equivalent toimpedance matching the resonant load to the characteristic impedance ofthe amplifier.

In a switching amplifier, the switching frequency of the switchingelements, f_(switch), wherein f_(switch)=ω/2π and the duty cycle, dc, ofthe ON switch-state duration of the switching elements may be the samefor all switching elements of the amplifier. In this specification, wewill use the term “class D” to denote both class D and class DEamplifiers, that is, switching amplifiers with dc<=50%.

The value of the characteristic impedance of the amplifier may depend onthe operating frequency, the amplifier topology, and the switchingsequence of the switching elements. In some embodiments, the switchingamplifier may be a half-bridge topology and, in some embodiments, afull-bridge topology. In some embodiments, the switching amplifier maybe class D and, in some embodiments, class E. In any of the aboveembodiments, assuming the elements of the bridge are symmetric, thecharacteristic impedance of the switching amplifier has the form

R _(O) =F _(R)(dc)/ωC _(α) ,X _(O) =F _(X)(dc)/ωC _(α),  (1)

where dc is the duty cycle of ON switch-state of the switching elements,the functions F_(R)(dc) and F_(X)(dc) are plotted in FIG. 7 (both forclass D and E), ω is the frequency at which the switching elements areswitched, and C_(α)=n_(α)C_(switc) where C_(switc) is the capacitanceacross each switch, including both the transistor output capacitance andalso possible external capacitors placed in parallel with the switch,while n_(α)=1 for a full bridge and n_(α)=2 for a half bridge. For classD, one can also write the analytical expressions

F _(R)(dc)=sin² u/π, F _(X)(dc)=(u−sin u*cos u)/π,  (2)

where u=π(1-2*dc), indicating that the characteristic impedance level ofa class D amplifier decreases as the duty cycle, dc, increases towards50%. For a class D amplifier operation with dc=50%, achieving ZVS andZCS is possible only when the switching elements have practically nooutput capacitance (C_(α)=0) and the load is exactly on resonance(X_(O)=0), while R_(O) can be arbitrary.

Impedance Matching Networks

In applications, the driven load may have impedance that is verydifferent from the characteristic impedance of the external drivingcircuit, to which it is connected. Furthermore, the driven load may notbe a resonant network. An Impedance Matching Network (IMN) is a circuitnetwork that may be connected before a load as in FIG. 6B, in order toregulate the impedance that is seen at the input of the networkconsisting of the IMN circuit and the load. An IMN circuit may typicallyachieve this regulation by creating a resonance close to the drivingfrequency. Since such an IMN circuit accomplishes all conditions neededto maximize the power transmission efficiency from the generator to theload (resonance and impedance matching—ZVS and ZCS for a switchingamplifier), in embodiments, an IMN circuit may be used between thedriving circuit and the load.

For an arrangement shown in FIG. 6B, let the input impedance of thenetwork consisting of the Impedance Matching Network (IMN) circuit andthe load (denoted together from now on as IMN+load) beZ_(l)=R_(l)(ω)+jX_(l)(ω). The impedance matching conditions of thisnetwork to the external circuit with characteristic impedanceZ_(O)=R_(O)−jX_(O) are then R_(l)(ω)=R_(O), X_(l)(ω)=X_(O).

Methods for Tunable Impedance Matching of a Variable Load

In embodiments where the load may be variable, impedance matchingbetween the load and the external driving circuit, such as a linear orswitching power amplifier, may be achieved by using adjustable/tunablecomponents in the IMN circuit that may be adjusted to match the varyingload to the fixed characteristic impedance Z_(O) of the external circuit(FIG. 6B). To match both the real and imaginary parts of the impedancetwo tunable/variable elements in the IMN circuit may be needed.

In embodiments, the load may be inductive (such as a resonator coil)with impedance R+jωL, so the two tunable elements in the IMN circuit maybe two tunable capacitance networks or one tunable capacitance networkand one tunable inductance network or one tunable capacitance networkand one tunable mutual inductance network.

In embodiments where the load may be variable, the impedance matchingbetween the load and the driving circuit, such as a linear or switchingpower amplifier, may be achieved by using adjustable/tunable componentsor parameters in the amplifier circuit that may be adjusted to match thecharacteristic impedance Z_(O) of the amplifier to the varying (due toload variations) input impedance of the network consisting of the IMNcircuit and the load (IMN+load), where the IMN circuit may also betunable (FIG. 6C). To match both the real and imaginary parts of theimpedance, a total of two tunable/variable elements or parameters in theamplifier and the IMN circuit may be needed. The disclosed impedancematching method can reduce the required number of tunable/variableelements in the IMN circuit or even completely eliminate the requirementfor tunable/variable elements in the IMN circuit. In some examples, onetunable element in the power amplifier and one tunable element in theIMN circuit may be used. In some examples, two tunable elements in thepower amplifier and no tunable element in the IMN circuit may be used.

In embodiments, the tunable elements or parameters in the poweramplifier may be the frequency, amplitude, phase, waveform, duty cycleand the like of the drive signals applied to transistors, switches,diodes and the like.

In embodiments, the power amplifier with tunable characteristicimpedance may be a tunable switching amplifier of class D, E, F or anycombinations thereof. Combining Equations (1) and (2), the impedancematching conditions for this network are

R _(l)(ω)=F _(R)(dc)/ωC _(α) , X _(l)(ω)=F _(X)(dc)/ωC _(α)  (3).

In some examples of a tunable switching amplifier, one tunable elementmay be the capacitance C_(α), which may be tuned by tuning the externalcapacitors placed in parallel with the switching elements.

In some examples of a tunable switching amplifier, one tunable elementmay be the duty cycle dc of the ON switch-state of the switchingelements of the amplifier. Adjusting the duty cycle, dc, via Pulse WidthModulation (PWM) has been used in switching amplifiers to achieve outputpower control. In this specification, we disclose that PWM may also beused to achieve impedance matching, namely to satisfy Eqs. (3), and thusmaximize the amplifier efficiency.

In some examples of a tunable switching amplifier one tunable elementmay be the switching frequency, which is also the driving frequency ofthe IMN+load network and may be designed to be substantially close tothe resonant frequency of the IMN+load network. Tuning the switchingfrequency may change the characteristic impedance of the amplifier andthe impedance of the IMN+load network. The switching frequency of theamplifier may be tuned appropriately together with one more tunableparameters, so that Eqs. (3) are satisfied.

A benefit of tuning the duty cycle and/or the driving frequency of theamplifier for dynamic impedance matching is that these parameters can betuned electronically, quickly, and over a broad range. In contrast, forexample, a tunable capacitor that can sustain a large voltage and has alarge enough tunable range and quality factor may be expensive, slow orunavailable for with the necessary component specifications

Examples of Methods for Tunable Impedance Matching of a Variable Load

A simplified circuit diagram showing the circuit level structure of aclass D power amplifier 802, impedance matching network 804 and aninductive load 806 is shown in FIG. 8. The diagram shows the basiccomponents of the system with the switching amplifier 804 comprising apower source 810, switching elements 808, and capacitors. The impedancematching network 804 comprising inductors and capacitors, and the load806 modeled as an inductor and a resistor.

An exemplary embodiment of this inventive tuning scheme comprises ahalf-bridge class-D amplifier operating at switching frequency f anddriving a low-loss inductive element R+jωL via an IMN, as shown in FIG.8.

In some embodiments L′ may be tunable. L′ may be tuned by a variabletapping point on the inductor or by connecting a tunable capacitor inseries or in parallel to the inductor. In some embodiments C_(α) may betunable. For the half bridge topology, C_(α) may be tuned by varyingeither one or both capacitors C_(switc), as only the parallel sum ofthese capacitors matters for the amplifier operation. For the fullbridge topology, C_(α) may be tuned by varying either one, two, three orall capacitors C_(switc), as only their combination (series sum of thetwo parallel sums associated with the two halves of the bridge) mattersfor the amplifier operation.

In some embodiments of tunable impedance matching, two of the componentsof the IMN may be tunable. In some embodiments, L′ and C₂ may be tuned.Then, FIG. 9 shows the values of the two tunable components needed toachieve impedance matching as functions of the varying R and L of theinductive element, and the associated variation of the output power (atgiven DC bus voltage) of the amplifier, for f=250 kHz, dc=40%, C_(α)=640pF and C₁=10 nF. Since the IMN always adjusts to the fixedcharacteristic impedance of the amplifier, the output power is alwaysconstant as the inductive element is varying.

In some embodiments of tunable impedance matching, elements in theswitching amplifier may also be tunable. In some embodiments thecapacitance C_(α) along with the IMN capacitor C₂ may be tuned. Then,FIG. 10 shows the values of the two tunable components needed to achieveimpedance matching as functions of the varying R and L of the inductiveelement, and the associated variation of the output power (at given DCbus voltage) of the amplifier for f=250 kHz, dc=40%, C₁=10 nF andωL′=1000Ω. It can be inferred from FIG. 10 that C₂ needs to be tunedmainly in response to variations in L and that the output powerdecreases as R increases.

In some embodiments of tunable impedance matching, the duty cycle dcalong with the IMN capacitor C₂ may be tuned. Then, FIG. 11 shows thevalues of the two tunable parameters needed to achieve impedancematching as functions of the varying R and L of the inductive element,and the associated variation of the output power (at given DC busvoltage) of the amplifier for f=250 kHz, C_(α)=640 pF, C₁=10 nF andωL′=1000Ω. It can be inferred from FIG. 11 that C₂ needs to be tunedmainly in response to variations in L and that the output powerdecreases as R increases.

In some embodiments of tunable impedance matching, the capacitance C_(α)along with the IMN inductor L′ may be tuned. Then, FIG. 11A shows thevalues of the two tunable components needed to achieve impedancematching as functions of the varying R of the inductive element, and theassociated variation of the output power (at given DC bus voltage) ofthe amplifier for f=250 kHz, dc=40%, C₁=10 nF and C₂=7.5 nF. It can beinferred from FIG. 11A that the output power decreases as R increases.

In some embodiments of tunable impedance matching, the duty cycle dcalong with the IMN inductor L′ may be tuned. Then, FIG. 11B shows thevalues of the two tunable parameters needed to achieve impedancematching as functions of the varying R of the inductive element, and theassociated variation of the output power (at given DC bus voltage) ofthe amplifier for f=250 kHz, C_(α)=640 pF, C₁=10 nF and C₂=7.5 nF asfunctions of the varying R of the inductive element. It can be inferredfrom FIG. 11B that the output power decreases as R increases.

In some embodiments of tunable impedance matching, only elements in theswitching amplifier may be tunable with no tunable elements in the IMN.In some embodiments the duty cycle dc along with the capacitance C_(α)may be tuned. Then, FIG. 11C, shows the values of the two tunableparameters needed to achieve impedance matching as functions of thevarying R of the inductive element, and the associated variation of theoutput power (at given DC bus voltage) of the amplifier for f=250 kHz,C₁=1.0 nF, C₂=7.5 nF and ωL′=1000Ω. It can be inferred from FIG. 11Cthat the output power is a non-monotonic function of R. Theseembodiments may be able to achieve dynamic impedance matching whenvariations in L (and thus the resonant frequency) are modest.

In some embodiments, dynamic impedance matching with fixed elementsinside the IMN, also when L is varying greatly as explained earlier, maybe achieved by varying the driving frequency of the external frequency f(e.g. the switching frequency of a switching amplifier) so that itfollows the varying resonant frequency of the resonator. Using theswitching frequency f and the switch duty cycle dc as the two variableparameters, full impedance matching can be achieved as R and L arevarying without the need of any variable components. Then, FIG. 12 showsthe values of the two tunable parameters needed to achieve impedancematching as functions of the varying R and L of the inductive element,and the associated variation of the output power (at given DC busvoltage) of the amplifier for C_(α)=640 pF, C₁=10 nF, C₂=7.5 nF andL′=637 μH. It can be inferred from FIG. 12 that the frequency f needs tobe tuned mainly in response to variations in L, as explained earlier.

Tunable Impedance Matching for Systems of Wireless Power Transmission

In applications of wireless power transfer the low-loss inductiveelement may be the coil of a source resonator coupled to one or moredevice resonators or other resonators, such as repeater resonators, forexample. The impedance of the inductive element R+jωL may include thereflected impedances of the other resonators on the coil of the sourceresonator. Variations of R and L of the inductive element may occur dueto external perturbations in the vicinity of the source resonator and/orthe other resonators or thermal drift of components. Variations of R andL of the inductive element may also occur during normal use of thewireless power transmission system due to relative motion of the devicesand other resonators with respect to the source. The relative motion ofthese devices and other resonators with respect to the source, orrelative motion or position of other sources, may lead to varyingcoupling (and thus varying reflected impedances) of the devices to thesource. Furthermore, variations of R and L of the inductive element mayalso occur during normal use of the wireless power transmission systemdue to changes within the other coupled resonators, such as changes inthe power draw of their loads. All the methods and embodiments disclosedso far apply also to this case in order to achieve dynamic impedancematching of this inductive element to the external circuit driving it.

To demonstrate the presently disclosed dynamic impedance matchingmethods for a wireless power transmission system, consider a sourceresonator including a low-loss source coil, which is inductively coupledto the device coil of a device resonator driving a resistive load.

In some embodiments, dynamic impedance matching may be achieved at thesource circuit. In some embodiments, dynamic impedance matching may alsobe achieved at the device circuit. When full impedance matching isobtained (both at the source and the device), the effective resistanceof the source inductive element (namely the resistance of the sourcecoil R_(s) plus the reflected impedance from the device) isR=R_(s)√{square root over (1+U_(sd) ²)}. (Similarly the effectiveresistance of the device inductive element is R_(d)√{square root over(1+U_(sd) ²)}, where R_(d) is the resistance of the device coil.)Dynamic variation of the mutual inductance between the coils due tomotion results in a dynamic variation of U_(sd)=ωM_(sd)/√{square rootover (R_(s)R_(d))}. Therefore, when both source and device aredynamically tuned, the variation of mutual inductance is seen from thesource circuit side as a variation in the source inductive elementresistance R. Note that in this type of variation, the resonantfrequencies of the resonators may not change substantially, since L maynot be changing. Therefore, all the methods and examples presented fordynamic impedance matching may be used for the source circuit of thewireless power transmission system.

Note that, since the resistance R represents both the source coil andthe reflected impedances of the device coils to the source coil, inFIGS. 9-12, as R increases due to the increasing U, the associatedwireless power transmission efficiency increases. In some embodiments,an approximately constant power may be required at the load driven bythe device circuitry. To achieve a constant level of power transmittedto the device, the required output power of the source circuit may needto decrease as U increases. If dynamic impedance matching is achievedvia tuning some of the amplifier parameters, the output power of theamplifier may vary accordingly. In some embodiments, the automaticvariation of the output power is preferred to be monotonicallydecreasing with R, so that it matches the constant device powerrequirement. In embodiments where the output power level is accomplishedby adjusting the DC driving voltage of the power generator, using animpedance matching set of tunable parameters which leads tomonotonically decreasing output power vs. R will imply that constantpower can be kept at the power load in the device with only a moderateadjustment of the DC driving voltage. In embodiments, where the “knob”to adjust the output power level is the duly cycle de or the phase of aswitching amplifier or a component inside an Impedance Matching Network,using an impedance matching set of tunable parameters which leads tomonotonically decreasing output power vs. R will imply that constantpower can be kept at the power load in the device with only a moderateadjustment of this power “knob”.

In the examples of FIGS. 9-12, if R_(s)=0.19Ω, then the range R=0.2-2Ωcorresponds approximately to U_(sd)=0.3-10.5. For these values, in FIG.14, we show with dashed lines the output power (normalized to DC voltagesquared) required to keep a constant power level at the load, when bothsource and device are dynamically impedance matched. The similar trendbetween the solid and dashed lines explains why a set of tunableparameters with such a variation of output power may be preferable.

In some embodiments, dynamic impedance matching may be achieved at thesource circuit, but impedance matching may not be achieved or may onlypartially be achieved at the device circuit. As the mutual inductancebetween the source and device coils varies, the varying reflectedimpedance of the device to the source may result in a variation of boththe effective resistance R and the effective inductance L of the sourceinductive element. The methods presented so far for dynamic impedancematching are applicable and can be used for the tunable source circuitof the wireless power transmission system.

As an example, consider the circuit of FIG. 14, where f=250 kHz,C_(α)=640 pF, R_(s)=0.19Ω, L_(s)=100 μH, C_(1s)=10 nF, ωL′_(s)=1000Ω,R_(d)=0.3Ω, L_(d)=40 μH, C_(1d)=87.5 nF, C_(2d)=13 nF, ωL′_(d)=400Ω andZ_(l)=50Ω, where s and d denote the source and device resonatorsrespectively and the system is matched at U_(sd)=3. Tuning the dutycycle dc of the switching amplifier and the capacitor C_(2s) may be usedto dynamically impedance match the source, as the non-tunable device ismoving relatively to the source changing the mutual inductance M betweenthe source and the device. In FIG. 14, we show the required values ofthe tunable parameters along with the output power per DC voltage of theamplifier. The dashed line again indicates the output power of theamplifier that would be needed so that the power at the load is aconstant value.

In some embodiments, tuning the driving frequency f of the sourcedriving circuit may still be used to achieve dynamic impedance matchingat the source for a system of wireless power transmission between thesource and one or more devices. As explained earlier, this methodenables full dynamic impedance matching of the source, even when thereare variations in the source inductance L_(s) and thus the sourceresonant frequency. For efficient power transmission from the source tothe devices, the device resonant frequencies must be tuned to follow thevariations of the matched driving and source-resonant frequencies.Tuning a device capacitance (for example, in the embodiment of FIG. 13C_(1d) or C_(2d)) may be necessary, when there are variations in theresonant frequency of either the source or the device resonators. Infact, in a wireless power transfer system with multiple sources anddevices, tuning the driving frequency alleviates the need to tune onlyone source-object resonant frequency, however, all the rest of theobjects may need a mechanism (such as a tunable capacitance) to tunetheir resonant frequencies to match the driving frequency.

Resonator Thermal Management

In wireless energy transfer systems, some portion of the energy lostduring the wireless transfer process is dissipated as heat. Energy maybe dissipated in the resonator components themselves. For example, evenhigh-Q conductors and components have some loss or resistance, and theseconductors and components may heat up when electric currents and/orelectromagnetic fields flow through them. Energy may be dissipated inmaterials and objects around a resonator. For example, eddy currentsdissipated in imperfect conductors or dielectrics surrounding or near-bythe resonator may heat up those objects. In addition to affecting thematerial properties of those objects, this heat may be transferredthrough conductive, radiative, or convective processes to the resonatorcomponents. Any of these heating effects may affect the resonator Q,impedance, frequency, etc., and therefore the performance of thewireless energy transfer system.

In a resonator comprising a block or core of magnetic material, heat maybe generated in the magnetic material due to hysteresis losses and toresistive losses resulting from induced eddy currents. Both effectsdepend on the magnetic flux density in the material, and both can createsignificant amounts of heat, especially in regions where the fluxdensity or eddy currents may be concentrated or localized. In additionto the flux density, the frequency of the oscillating magnetic field,the magnetic material composition and losses, and the ambient oroperating temperature of the magnetic material may all impact howhysteresis and resistive losses heat the material.

In embodiments, the properties of the magnetic material such as the typeof material, the dimensions of the block, and the like, and the magneticfield parameters may be chosen for specific operating power levels andenvironments to minimize heating of the magnetic material. In someembodiments, changes, cracks, or imperfections in a block of magneticmaterial may increase the losses and heating of the magnetic material inwireless power transmission applications.

For magnetic blocks with imperfections, or that are comprised of smallersize tiles or pieces of magnetic material arranged into a larger unit,the losses in the block may be uneven and may be concentrated in regionswhere there are inhomogeneities or relatively narrow gaps betweenadjacent tiles or pieces of magnetic material. For example, if anirregular gap exists in a magnetic block of material, then the effectivereluctance of various magnetic flux paths through the material may besubstantially irregular and the magnetic field may be more concentratedin portions of the block where the magnetic reluctance is lowest. Insome cases, the effective reluctance may be lowest where the gap betweentiles or pieces is narrowest or where the density of imperfections islowest. Because the magnetic material guides the magnetic field, themagnetic flux density may not be substantially uniform across the block,but may be concentrated in regions offering relatively lower reluctance.Irregular concentrations of the magnetic field within a block ofmagnetic material may not be desirable because they may result in unevenlosses and heat dissipation in the material.

For example, consider a magnetic resonator comprising a conductor 1506wrapped around a block of magnetic material composed of two individualtiles 1502, 1504 of magnetic material joined such that they form a seam1508 that is perpendicular to the axis of the conductor 1506 loops asdepicted in FIG. 15. An irregular gap in the seam 1508 between the tilesof magnetic material 1502, 1504 may force the magnetic field 1512(represented schematically by the dashed magnetic field lines) in theresonator to concentrate in a sub region 1510 of the cross section ofthe magnetic material. Since the magnetic field will follow the path ofleast reluctance, a path including an air gap between two pieces ofmagnetic material may create an effectively higher reluctance path thanone that traverses the width of the magnetic material at a point wherethe pieces of magnetic materials touch or have a smaller air gap. Themagnetic flux density may therefore preferentially flow through arelatively small cross area of the magnetic material resulting in a highconcentration of magnetic flux in that small area 1510.

In many magnetic materials of interest, more inhomogeneous flux densitydistributions lead to higher overall losses. Moreover, the moreinhomogeneous flux distribution may result in material saturation andcause localized heating of the area in which the magnetic flux isconcentrated. The localized heating may alter the properties of themagnetic material, in some cases exacerbating the losses. For example,in the relevant regimes of operation of some materials, hysteresis andresistive losses increase with temperature. If heating the materialincreases material losses, resulting in more heating, the temperature ofthe material may continue to increase and even runaway if no correctiveaction is taken. In some instances, the temperature may reach 100 C ormore and may degrade the properties of the magnetic material and theperformance of wireless power transfer. In some instances, the magneticmaterials may be damaged, or the surrounding electronic components,packaging and/or enclosures may be damaged by the excessive heat.

In embodiments, variations or irregularities between tiles or pieces ofthe block of magnetic material may be minimized by machining, polishing,grinding, and the like, the edges of the tiles or pieces to ensure atight fit between tiles of magnetic materials providing a substantiallymore uniform reluctance through the whole cross section of the block ofmagnetic material. In embodiments, a block of magnetic material mayrequire a means for providing a compression force between the tiles toensure the tiles are pressed tight together without gaps. Inembodiments, an adhesive may be used between the tiles to ensure theyremain in tight contact.

In embodiments the irregular spacing of adjacent tiles of magneticmaterial may be reduced by adding a deliberate gap between adjacenttiles of magnetic material. In embodiments a deliberate gap may be usedas a spacer to ensure even or regular separations between magneticmaterial tiles or pieces. Deliberate gaps of flexible materials may alsoreduce irregularities in the spacings due to tile movement orvibrations. In embodiments, the edges of adjacent tiles of magneticmaterial may be taped, dipped, coated, and the like with an electricalinsulator, to prevent eddy currents from flowing through reducedcross-sectional areas of the block, thus lowering the eddy currentlosses in the material. In embodiments a separator may be integratedinto the resonator packaging. The spacer may provide a spacing of 1 mmor less.

In embodiments, the mechanical properties of the spacer between tilesmay be chosen so as to improve the tolerance of the overall structure tomechanical effects such as changes in the dimensions and/or shape of thetiles due to intrinsic effects (e.g, magnetostriction, thermalexpansion, and the like) as well as external shocks and vibrations. Forexample, the spacer may have a desired amount of mechanical give toaccommodate the expansion and/or contraction of individual tiles, andmay help reduce the stress on the tiles when they are subjected tomechanical vibrations, thus helping to reduce the appearance of cracksand other defects in the magnetic material.

In embodiments, it may be preferable to arrange the individual tilesthat comprise the block of magnetic material to minimize the number ofseams or gaps between tiles that are perpendicular to the dipole momentof the resonator. In embodiments it may be preferable to arrange andorient the tiles of magnetic material to minimize the gaps between tilesthat are perpendicular to the axis formed by the loops of a conductorcomprising the resonator.

For example, consider the resonator structure depicted in FIG. 16. Theresonator comprises a conductor 1604 wrapped around a block of magneticmaterial comprising six separate individual tiles 1602 arranged in athree by two array. The arrangement of tiles results in two tile seams1606, 1608 when traversing the block of magnetic material in onedirection, and only one tile seam 1610 when traversing the block ofmagnetic material in the orthogonal direction. In embodiments, it may bepreferable to wrap the conductor wire 1604 around the block of magneticmaterial such that the dipole moment of the resonator is perpendicularto the fewest number of tile seams. The inventors have observed thatthere is relatively less heating induced around seams and gaps 1606,1608 that are parallel to the dipole moment of the resonator. Seams andgaps that run perpendicular to the dipole moment of the resonator mayalso be referred to as critical seams or critical seam areas. It maystill be desirable, however, to electrically insulate gaps that runparallel to the dipole moment of the resonator (such as 1606 and 1608)so as to reduce eddy current losses. Uneven contact between tilesseparated by such parallel gaps may cause eddy currents to flow throughnarrow contact points, leading to large losses at such points.

In embodiments, irregularities in spacing may be tolerated with adequatecooling of the critical seam areas to prevent the localized degradationof material properties when the magnetic material heats up. Maintainingthe temperature of the magnetic material below a critical temperaturemay prevent a runaway effect caused by a sufficiently high temperature.With proper cooling of the critical seam area, the wireless energytransfer performance may be satisfactory despite the additional loss andheating effects due to irregular spacing, cracks, or gaps between tiles.

Effective heatsinking of the resonator structure to prevent excessivelocalized heating of the magnetic material poses several challenges.Metallic materials that are typically used for heatsinks and thermalconduction can interact with the magnetic fields used for wirelessenergy transfer by the resonators and affect the performance of thesystem. Their location, size, orientation, and use should be designed soas to not excessively lower the perturbed Q of the resonators in thepresence of these heatsinking materials. In addition, owing to therelatively poor thermal conductivity of magnetic materials such asferrites, a relatively large contact area between the heatsink and themagnetic material may be required to provide adequate cooling which mayrequire placement of substantial amount of lossy materials close to themagnetic resonator.

In embodiments, adequate cooling of the resonator may be achieved withminimal effect on the wireless energy transfer performance withstrategic placement of thermally conductive materials. In embodiments,strips of thermally conductive material may be placed in between loopsof conductor wire and in thermal contact with the block of magneticmaterial.

One exemplary embodiment of a resonator with strips of thermallyconductive material is depicted in FIG. 17. FIG. 17A shows the resonatorstructure without the conducting strips and with the block of magneticmaterial comprising smaller tiles of magnetic material forming gaps orseams. Strips of thermally conductive 1708 material may be placed inbetween the loops of the conductor 1702 and in thermal contact with theblock of magnetic material 1704 as depicted in FIGS. 17B and 17C. Tominimize the effects of the strips on the parameters of the resonator,in some embodiments it may be preferable to arrange the strips parallelto the loops of conductor or perpendicular to the dipole moment of theresonator. The strips of conductor may be placed to cover as much or asmany of the seams or gaps between the tiles as possible especially theseams between tiles that are perpendicular to the dipole moment of theresonator.

In embodiments the thermally conductive material may comprise copper,aluminum, brass, thermal epoxy, paste, pads, and the like, and may beany material that has a thermal conductivity that is at least that ofthe magnetic material in the resonator (˜5 W/(K-m) for some commercialferrite materials). In embodiments where the thermally conductivematerial is also electrically conducting, the material may require alayer or coating of an electrical insulator to prevent shorting anddirect electrical contact with the magnetic material or the loops ofconductor of the resonator.

In embodiments the strips of thermally conductive material may be usedto conduct heat from the resonator structure to a structure or mediumthat can safely dissipate the thermal energy. In embodiments thethermally conductive strips may be connected to a heat sink such as alarge plate located above the strips of conductor that can dissipate thethermal energy using passive or forced convection, radiation, orconduction to the environment. In embodiments the system may include anynumber of active cooling systems that may be external or internal to theresonator structure that can dissipate the thermal energy from thethermally conducting strips and may include liquid cooling systems,forced air systems, and the like. For example, the thermally conductingstrips may be hollow or comprise channels for coolant that may be pumpedor forced through to cool the magnetic material. In embodiments, a fielddeflector made of a good electrical conductor (such as copper, silver,aluminum, and the like) may double as part of the heatsinking apparatus.The addition of thermally and electrically conducting strips to thespace between the magnetic material and the field deflector may have amarginal effect on the perturbed Q, as the electromagnetic fields inthat space are typically suppressed by the presence of the fielddeflector. Such conducting strips may be thermally connected to both themagnetic material and the field deflector to make the temperaturedistribution among different strips more homogeneous.

In embodiments the thermally conducting strips are spaced to allow atleast one loop of conductor to wrap around the magnetic material. Inembodiments the strips of thermally conductive material may bepositioned only at the gaps or seams of the magnetic material. In otherembodiments, the strips may be positioned to contact the magneticmaterial at substantially throughout its complete length. In otherembodiments, the strips may be distributed to match the flux densitywithin the magnetic material. Areas of the magnetic material which undernormal operation of the resonator may have higher magnetic fluxdensities may have a higher density of contact with the thermallyconductive strips. In embodiments depicted in FIG. 17A) for example, thehighest magnetic flux density in the magnetic material may be observedtoward the center of the block of magnetic material and the lowerdensity may be toward the ends of the block in the direction of thedipole moment of the resonator.

To show how the use of thermally conducting strips helps to reduce theoverall temperature in the magnetic material as well as the temperatureat potential hot spots, the inventors have performed a finite elementsimulation of a resonator structure similar to that depicted in FIG.17C. The structure was simulated operating at a frequency of 235 kHz andcomprising a block of EPCOS N95 magnetic material measuring 30 cm×30cm×5 mm excited by 10 turns of litz wire (symmetrically placed at 25 mm,40 mm, 55 mm, 90 mm and 105 mm from the plane of symmetry of thestructure) carrying 40 A of peak current each, and thermally connectedto a 50 cm×50 cm×4 mm field deflector by means of three 3×¾×1′ hollowsquare tubes (⅛″ wall thickness) of aluminum (alloy 6063) whose centralaxes are placed at −75 mm, 0 mm, and +75 from the symmetry plane of thestructure. The perturbed Q due to the field deflector and hollow tubeswas found to be 1400 (compared to 1710 for the same structure withoutthe hollow tubes). The power dissipated in the shield and tubes wascalculated to be 35.6 W, while that dissipated in the magnetic materialwas 58.3 W. Assuming the structure is cooled by air convection andradiation and an ambient temperature of 24° C., the maximum temperaturein the structure was 85° C. (at points in the magnetic materialapproximately halfway between the hollow tubes) while the temperature inparts of the magnetic material in contact with the hollow tubes wasapproximately 68° C. By comparison, the same resonator without thethermally conducting hollow tubes dissipated 62.0 W in the magneticmaterial for the same excitation current of 40 W peak and the maximumtemperature in the magnetic material was found to be 111° C.

The advantage of the conducting strips is more apparent still if weintroduce a defect in a portion of the magnetic material that is in goodthermal contact with the tubes. An air gap 10 cm long and 0.5 mm placedat the center of the magnetic material and oriented perpendicular to thedipole moment increases the power dissipated in the magnetic material to69.9 W (the additional 11.6 W relative to the previously discussedno-defect example being highly concentrated in the vicinity of the gap),but the conducting tube ensures that the maximum temperature in themagnetic material has only a relative modest increase of 11° C. to 96°C. In contrast, the same defect without the conducting tubes leads to amaximum temperature of 161° C. near the defect. Cooling solutions otherthan convection and radiation, such as thermally connecting theconducting tubes body with large thermal mass or actively cooling them,may lead to even lower operational temperatures for this resonator atthe same current level.

In embodiments thermally conductive strips of material may be positionedat areas that may have the highest probability of developing cracks thatmay cause irregular gaps in the magnetic material. Such areas may beareas of high stress or strain on the material, or areas with poorsupport or backing from the packaging of the resonator. Strategicallypositioned thermally conductive strips may ensure that as cracks orirregular gaps develop in the magnetic material, the temperature of themagnetic material will be maintained below its critical temperature. Thecritical temperature may be defined as the Curie temperature of themagnetic material, or any temperature at which the characteristics ofthe resonator have been degraded beyond the desired performanceparameters.

In embodiments the heastsinking structure may provide mechanical supportto the magnetic material. In embodiments the heatsinking structure maybe designed to have a desired amount of mechanical give (e.g., by usingepoxy, thermal pads, and the like having suitable mechanical propertiesto thermally connect different elements of the structure) so as toprovide the resonator with a greater amount of tolerance to changes inthe intrinsic dimensions of its elements (due to thermal expansion,magnetostriction, and the like) as well as external shocks andvibrations, and prevent the formation of cracks and other defects.

In embodiments where the resonator comprises orthogonal windings wrappedaround the magnetic material, the strips of conducting material may betailored to make thermal contact with the magnetic material within areasdelimited by two orthogonal sets of adjacent loops. In embodiments astrip may contain appropriate indentations to fit around the conductorof at least one orthogonal winding while making thermal contact with themagnetic material at least one point. In embodiments the magneticmaterial may be in thermal contact with a number of thermally conductingblocks placed between adjacent loops. The thermally conducting blocksmay be in turn thermally connected to one another by means of a goodthermal conductor and/or heatsinked.

Throughout this description although the term thermally conductivestrips of material was used as an exemplary specimen of a shape of amaterial it should be understood by those skilled in the art that anyshapes and contours may be substituted without departing from the spiritof the inventions. Squared, ovals, strips, dots, elongated shapes, andthe like would all be within the spirit of the present invention.

Communication in a Wireless Energy Transfer System

A wireless energy transfer system may require a verification step toensure that energy is being transferred between designated resonators.For example, in wireless energy transfer systems, source resonators,device resonators, and repeater resonators, do not require physicalcontact with each other in order to exchange energy, and theseresonators may be separated from each other by distances of centimetersor meters, depending on the size and number of resonators in the system.In some configurations, multiple resonators may be in a position togenerate or receive power, but only two or some of those resonators aredesignated resonators.

Communication of information between resonators in a wireless energytransfer system may be utilized to designate resonators. Communicationof information between resonators may be implemented using in-band orout-of-band communications or communications channels. If at least somepart of a magnetic resonator used to exchange power is also used toexchange information, and the carrier frequency of the informationexchange is close to the resonant frequency used in the power exchange,we refer to that communication as in-band. Any other type ofcommunication between magnetic resonators is referred to as out-of-band.An out-of-band communication channel may use an antenna and a signalingprotocol that is separated from the energy transfer resonator andmagnetic fields. An out-of-band communication channel may use or bebased on Bluetooth, WiFi, Zigbee, NFC technology and the like.

Communication between resonators may be used to coordinate the wirelessenergy transfer or to adjust the parameters of a wireless energytransfer system, to identify and authenticate available power sourcesand devices, to optimize efficiency, power delivery, and the like, totrack and bill energy preferences, usage, and the like, and to monitorsystem performance, battery condition, vehicle health, extraneousobjects, also referred to as foreign objects, and the like. Methods fordesignating and verifying resonators for energy transfer may bedifferent when in-band and out-of-band communication channels are usedbecause the distance over which communication signals may be exchangedusing out-of-band techniques may greatly exceed the distance over whichthe power signals may be exchanged. Also, the bandwidth of out-of-bandcommunication signals may be larger than in-band communication signals.This difference in communication range and capability may affect thecoordination of the wireless energy transfer system. For example, thenumber of resonators that may be addressed using out-of-bandcommunication may be very large and communicating resonators may befarther apart than the distance over which they may efficiently exchangeenergy.

In some embodiments all of the signaling and communication may beperformed using an in-band communication channel and the signals may bemodulated on the fields used for energy transfer. In other embodiments,in-band communication may use substantially the same frequency spectrumas is used for energy transfer, but communication may occur while usefulamounts of energy are not being transmitted. Using only the in-bandcommunication channel may be preferable if separate or multipleverification steps are problematic, because the range of thecommunication may be limited to the same range as the power exchange orbecause the information arrives as a modulation on the power signalitself. In some embodiments however, a separate out-of-bandcommunication channel may be more desirable. For example, an out-of-bandcommunication channel may be less expensive to implement and may supporthigher data rates. An out-of-band communication channel may supportlonger distance communication, allowing resonator discovery and powersystem mapping. An out-of-band communication channel may operateregardless of whether or not power transfer is taking place and mayoccur without disruption of the power transfer.

An exemplary embodiment of a wireless energy system is shown in FIG. 18.This exemplary embodiment comprises two device resonators 1802, 1816each with an out-of-band communication module 1804, 1818 respectivelyand two source resonators 1806, 1810 each with their own out-of-bandcommunication modules 1808, 1812 respectively. The system may use theout-of-band communication channel to adjust and coordinate the energytransfer. The communication channel may be used to discover or findresonators in the proximity, to initiate power transfer, and tocommunicate adjustment of operating parameters such as power output,impedance, frequency, and the like of the individual resonators.

In some situations a device resonator may incorrectly communicate withone source but receive energy from another source resonator. Forexample, imagine that device 1802 sends an out-of-band communicationsignal requesting power from a source. Source 1810 may respond and beginto supply power to device 1802. Imagine that device 1816 also sends anout-of-band communication signal requesting power from a source and thatsource 1806 responds and begins to supply power to device 1816. Becauseof the proximity of device 1802 to source 1806, it is possible thatdevice 1802 receives some or most of its power from source 1806. If thepower level received by device 1802 becomes too high, device 1802 maysend an out-of-band communication signal to source 1810 to reduce thepower it is transmitting to device 1802. However, device 1802 may stillbe receiving too much power, because it is receiving power from source1806 but is not communicating control signals to that source 1806.

Therefore, the separation of the energy transfer channel and thecommunication channel may create performance, control, safety, security,reliability, and the like issues in wireless energy transfer systems. Inembodiments, it may be necessary for resonators in a wireless energytransfer system to identify/designate and verify any and all resonatorswith which it is exchanging power. As those skilled in the art willrecognize, the example shown in FIG. 18 is just one example and thereexist many configurations and arrangements of wireless powertransmission systems that may benefit from explicit or implicit energytransfer verification steps.

In embodiments, the potential performance, control, safety, security,reliability and the like, issues may be avoided by providing at leastone verification step that insures that the energy transfer channel andthe communication channel used by a pair of resonators are associatedwith the same pair of resonators.

In embodiments the verification step may comprise some additionalinformation exchange or signaling through the wireless energy transferchannel. A verification step comprising communication or informationexchange using the energy transfer channel, or fields of the energytransfer channel may be used to verify that the out-of-bandcommunication channel is exchanging information between the same tworesonators that are or will be exchanging energy.

In embodiments with an out-of-band communication channel theverification step may be implicit or explicit. In sonic embodimentsverification may be implicit. In embodiments an energy transfer channelmay be implicitly verified by monitoring and comparing the behavior ofthe energy transfer channel to expected behavior or parameters inresponse to the out-of-band information exchange. For example, afterestablishing out-of-band communications, a device may request that awireless source increase the amount of power it is transmitting. At thesame time, parameters of the wireless energy transfer channel andresonators may be monitored. An observed increase of delivered power atthe device may be used to infer that the out-of-band communicationchannel and the energy transfer channel are correctly linked to thedesignated resonators.

In embodiments an implicit verification step may involve monitoring anynumber of the parameters of the wireless energy transfer or parametersof the resonators and components used in the wireless energy transfer.In embodiments the currents, voltages, impedances, frequency,efficiency, temperatures, of the resonators and their drive circuits andthe like may be monitored and compared to expected values, trends,changes and the like as a result of an out-of-band communicationexchange.

In embodiments a resonator may store tables of measured parameters andexpected values, trends, and/or changes to these parameters as aconsequence of a communication exchange. A resonator may store a historyof communications and observed parameter changes that may be used toverify the energy transfer channel. In some cases a single unexpectedparameter change due to a communication exchange may be not beconclusive enough to determine the out-of-band channel is incorrectlypaired. In some embodiments the history of parameter changes may bescanned or monitored over several or many communication exchanges toperform verification.

An example algorithm showing the series of steps which may be used toimplicitly verify an energy transfer channel in a wireless energytransfer system using out-of-band communication is shown in FIG. 19A. Inthe first step 1902 an out-of-band communication channel between asource and a device is established. In the next step 1904 the source anddevice may exchange information regarding adjusting the parameters ofthe wireless energy transfer or parameters of the components used forwireless energy transfer. The information exchange on the out-of-bandcommunication channel may be a normal exchange used in normal operationof the system to control and adjust the energy transfer. In some systemsthe out-of-band communication channel may be encrypted preventingeavesdropping, impersonation, and the like. In the next step 1906 thesource and the device or just a source or just a device may monitor andkeep track of any changes to the parameters of the wireless energytransfer or any changes in parameters in the components used in theenergy transfer. The tracked changes may be compared against expectedchanges to the parameters as a consequence of any out-of-bandcommunication exchanges. Validation may be considered failed when one ormany observed changes in parameters do not correspond to expectedchanges in parameters.

In some embodiments of wireless energy transfer systems verification maybe explicit. In embodiments a source or a device may alter, dither,modulate, and the like the parameters of the wireless energy transfer orthe parameters of the resonators used in the wireless energy transfer tocommunicate or provide a verifiable signal to a source or device throughthe energy transfer channel. The explicit verification may involvechanging, altering, modulating, and the like some parameters of thewireless energy transfer or the parameters of the resonators andcomponents used in the energy transfer for the explicit purpose ofverification and may not be associated with optimizing, tuning, oradjusting the energy transfer.

The changing, altering, modulating, and the like some parameters of thewireless energy transfer or the parameters of the resonators andcomponents used in the energy transfer for the purpose of signaling orcommunicating with another wireless energy resonator or component mayalso be referred to as in-band communication. In embodiments, thein-band communication channel may be implemented as part of the wirelessenergy transfer resonators and components. Information may betransmitted from one resonator to another by changing the parameters ofthe resonators. Parameters such as inductance, impedance, resistance,and the like may be dithered or changed by one resonator. These changesmay affect the impedance, resistance, or inductance of other resonatorsaround the signaling resonator. The changes may manifest themselves ascorresponding dithers of voltage, current, and the like on theresonators which may be detected and decoded into messages. Inembodiments, in-band communication may comprise altering, changing,modulating, and the like the power level, amplitude, phase, orientation,frequency, and the like of the magnetic fields used for energy transfer.

In one embodiment the explicit in-band verification may be performedafter an out-of-band communication channel has been established. Usingthe out-of-band communication channel a source and a device may exchangeinformation as to the power transfer capabilities and in-band signalingcapabilities. Wireless energy transfer between a source and a device maythen be initiated. The source or device may request or challenge theother source or device to signal using the in-band communication channelto verify the connection between the out-of-band and communicationchannel and the energy transfer channel. The channel is verified whenthe agreed signaling established in the out-of-band communicationchannel is observed at the in-band communication channel.

In embodiments verification may be performed only during specific orpre-determined times of an energy exchange protocol such as duringenergy transfer startup. In other embodiments explicit verificationsteps may be performed periodically during the normal operation of thewireless energy transfer system. The verification steps may be triggeredwhen the efficiency or characteristics of the wireless power transferchange which may signal that the physical orientations have changed. Inembodiments the communication controller may maintain a history of theenergy transfer characteristics and initiate a verification of thetransfer that includes signaling using the resonators when a change inthe characteristics is observed. A change in the energy transfercharacteristics may be observed as a change in the efficiency of theenergy transfer, the impedance, voltage, current, and the like of theresonators, or components of the resonators and power and controlcircuitry.

Those skilled in the art wilt appreciate a signaling and communicationchannel capable of transmitting messages may be secured with any numberof encryption, authentication, and security algorithms. In embodimentsthe out-of-band communication may be encrypted and the securedcommunication channel may be used to transmit random sequences forverification using the in-band channel. In embodiments the in-bandcommunication channel may be encrypted, randomized, or secured by anyknown security and cryptography protocols and algorithms. The securityand cryptography algorithms may be used to authenticate and verifycompatibility between resonators and may use a public key infrastructure(PKI) and secondary communication channels for authorization andauthentication.

In embodiments of energy transfer systems between a source and a devicea device may verify the energy transfer channel to ensure it isreceiving energy from the desired or assumed source. A source may verifythe energy transfer channel to ensure energy is being transferred to thedesired or assumed source. In some embodiments the verification may bebidirectional and a source and device may both verify their energytransfer channels in one step or protocol operation. In embodiments,there may be more than two resonators and there may be repeaterresonators. In embodiments of multiple resonators, communication andcontrol may be centralized in one or a few resonators or communicationand control may be distributed across many, most, or all the resonatorsin a network. In embodiments, communication and/or control may beeffected by one or more semiconductor chips or microcontrollers that arecoupled to other wireless energy transfer components.

An example algorithm showing the series of steps which may be used toexplicitly verify an energy transfer channel in a wireless energytransfer system using out-of-band communication is shown in FIG. 19B. Inthe first step 1908 an out-of-band communication channel between asource and a device is established. In the next step 1910 the source anddevice may coordinate or agree on a signaling protocol, method, scheme,and the like that may be transmitted through the wireless energytransfer channel. To prevent eavesdropping and provide security theout-of-band communication channel may be encrypted and the source anddevice may follow any number of known cryptographic authenticationprotocols. In a system enabled with cryptographic protocols theverification code may comprise a challenge-response type exchange whichmay provide an additional level of security and authenticationcapability. A device, for example, may challenge the source to encrypt arandom verification code which it sends to the source via theout-of-band communication channel using a shared secret encryption keyor a private key. The verification code transmitted in the out-of-bandcommunication channel may then be signaled 1912 through the in-bandcommunication channel. In the case where the source and device areenabled with cryptographic protocols the verification code signaled inthe in-band communication channel may be encrypted or modified by thesender with a reversible cryptographic function allowing the receiver tofurther authenticate the sender and verify that the in-bandcommunication channels are linked with the same source or deviceassociated with the out-of-band communication channel.

In situations when the verification fails a wireless energy transfersystem may try to repeat the validation procedure. In some embodimentsthe system may try to re-validate the wireless energy transfer channelby exchanging another verification sequence for resignaling using thein-band communication channel. In some embodiments the system may changeor alter the sequence or type of information that is used to verify thein-band communication channel after attempts to verify the in-bandcommunication channel have failed. The system may change the type ofsignaling, protocol, length, complexity and the like of the in-bandcommunication verification code.

In some embodiments, upon failure of verification of the in-bandcommunication channel and hence the energy transfer channel, the systemmay adjust the power level, the strength of modulation, frequency ofmodulation and the like of the signaling method in the in-bandcommunication channel. For example, upon failure of verification of asource by a device, the system may attempt to perform the verificationat a higher energy transfer level. The system may increase the poweroutput of the source generating stronger magnetic fields. In anotherexample, upon failure of verification of a source by a device, thesource that communicated the verification code to the device by changingthe impedance of its source resonator may increase or even double theamount of change in the impedance of the source resonator for thesignaling.

In embodiments, upon failure of verification of the energy transferchannel, the system may try to probe, find, or discover other possiblesources or devices using the out-of-band communication channel. Inembodiments the out-of-band communication channel may be used to findother possible candidates for wireless energy transfer. In someembodiments the system may change or adjust the output power or therange of the out-of-band communication channel to help minimize falsepairings.

The out-of-band communication channel may be power modulated to haveseveral modes, long range mode to detect sources and a short range orlow power mode to ensure the communication is with another device orsource that is within a specified distance. In embodiments theout-of-band communication channel may be matched to the range of thewireless channel for each application. After failure of verification ofthe energy transfer channel the output power of the out-of-bandcommunication channel may be slowly increased to find other possiblesources or devices for wireless energy transfer. As discussed above, anout-of-band communication channel may exhibit interferences andobstructions that may be different from the interferences andobstructions of the energy transfer channel and sources and devices thatmay require higher power levels for out-of-band communication may be inclose enough proximity to allow wireless energy transfer.

In some embodiments the out-of-band communication channel may bedirected, arranged, focused, and the like, using shielding orpositioning to be only effective in a confined area (i.e., under avehicle), to insure it is only capable of establishing communicationwith another source or device that is in close enough proximity,position, and orientation for energy transfer.

In embodiments the system may use one or more supplemental sources ofinformation to establish an out-of-band communication channel or toverify an in-band energy transfer channel. For example, during initialestablishment of an out-of-band communication channel the locations ofthe sources or devices may be compared to known or mapped locations or adatabase of locations of wireless sources or devices to determine themost probable pair for successful energy transfer. Out-of-bandcommunication channel discovery may be supplemented with GPS data fromone or more GPS receivers, data from positioning sensors, inertialguidance systems and the like.

It is to be understood that although example embodiments withverification were described in systems consisting of a source and deviceverification may be performed in systems with any number of sources,devices, or repeaters. A single source may provide verification tomultiple devices. In some embodiments multiple sources may provide powerto one or more devices concurrently each may be varied. In embodimentsverification may be performed with a repeater. In some embodimentsverification may be performed through a repeater. A device receivingpower from a source via a repeater resonator may verify the source ofpower from the repeater. A device receiving power from a source via arepeater resonator may verify the source of energy through the repeater,i.e., the in-band communication may pass through the repeater to thesource for verification. It should be clear to those skilled in the artthat all of these and other configurations are within the scope of theinvention.

Low Resistance Electrical Conductors

As described above, resonator structures used for wireless energytransfer may include conducting wires that conduct high frequencyoscillating currents. In some structures the effective resistance of theconductors may affect the quality factor of the resonator structure anda conductor with a tower loss or lower resistance may be preferable. Theinventors have discovered new structures thr reducing the effectiveresistance of conducting wires at high frequencies compared to solidwire conductors or even Litz wire conductors of the same equivalent wiregauge (diameter).

In embodiments, structures comprising concentric cylindrical conductingshells can be designed that have much lower electrical resistance forfrequencies in the MHz range than similarly sized solid wire conductorsor commercially available Litz wires. At such frequencies, wireresistances are dominated by skin-depth effects (also referred to asproximity effects), which prevent electrical current from beinguniformly distributed over the wire cross-section. At lower frequencies,skin-depth effects may be mitigated by breaking the wire into a braid ofmany thin insulated wire strands (e.g. Litz wire), where the diameter ofthe insulated strands are related to the conductor skin depth at theoperating frequency of interest. In the MHz frequency range, the skindepth for typical conductors such as copper are on the order of 10 μm,making traditional Litz wire implementations impractical.

The inventors have discovered that breaking the wire into multipleproperly designed concentric insulated conducting shells can mitigatethe skin depth effects for frequencies above 1 MHz. In embodiments,wires comprising fewer than 10 coaxial shells can lower AC resistance bymore than a factor of 3 compared to solid wire. In embodiments, wires orconductors comprising thin concentric shells can be fabricated by avariety of processes such as electroplating, electrodeposition, vapordeposition, sputtering, and processes that have previously been appliedto the fabrication of optical fibers.

In embodiments, conducting structures comprising nested cylindricalconductors may be analyzed using the quasistatic Maxwell equations. Ofparticular importance in the design of these conducting structures istaking account of the proximity losses induced by each conducting shellin the others via the magnetic fields. Modeling tools may be used tooptimize the number of conducting shells, the size and shape of theconducting shells, the type and thickness of insulating materials for agiven conductor diameter, operating frequency and environment, cost, andthe like.

One embodiment of the new conductor structure comprises a number, N, ofconcentric conducting shells. Such a structure can be designed to havemuch lower AC resistance at frequencies in the 10 MHz range than similargauge solid or stranded wires or commercially available Litz wires.

An embodiment of a wire or conductor comprising conducting shells maycomprise at least two concentric conducting shells separated by anelectrical insulator. An exemplary embodiment of an electrical conductorwith four concentric shells is shown in FIG. 20. Note that the conductormay have an unlimited length along the z axis. That is, the length alongthe z axis is the length of the wire or the conductor. Also, the wire orconductor may have any number of bends, curves, twists, and the like(not shown) as would other conductors of equivalent gauge or thickness.Also note that in embodiments where the cross-section of the shell isannular or substantially annular, the shell will consequently becylindrical or substantially cylindrical. There is no limitation to theshape of the cross sections and thus the shape of the resultingthree-dimensional structure. For example, the cross-sectional shape maybe rectangular in embodiments.

An embodiment shown in FIG. 20 comprises four concentric shells 2008,2006, 2004, 2002 of an electrical conductor that extend through thecomplete length of the conducting wire along the z axis. The conductorshells may be referred to by their location with respect to the centeror innermost conductor shell. For convention, the innermost shell may bereferred to as the first shell, and each successive shell as the secondshell, third shell, etc. The successive shells may also referred to asnested concentric shells. For example, in the embodiment shown in FIG.20 conductor shell 2002 may be referred to as the first shell or theinnermost shell and the conductor 2004 as the second shell, conductor2006 as the third shell, and conductor 2008 as the fourth shell or theoutermost shell. Each shell, except the innermost and the outermostshell, is in direct proximity to two neighboring shells, an innerneighbor and an outer neighbor shell. The innermost shell only has anouter neighbor, and the outermost shell only has an inner neighbor. Forexample, the third conductor 2006 has two shell neighbors, the innerneighbor being the second shell 2004 and the outer neighbor being thefourth shell 2008. In embodiments, the inner shell may be a solid core(in embodiments, cylindrical with an inner diameter zero).Alternatively, it may have a finite inner diameter and surround a coremade of insulating material and the like.

In embodiments each successive shell covers its inner neighbor shelllong the z axis of the conductor. Each shell wraps around its innerneighbor shell except the faces of each shell that are exposed at theends of the conductor. For example, in the embodiment shown in FIG. 20,shell 2002 is wrapped around by its outer neighbor shell 2004 and shell2004 is wrapped by 2006 and etc.

In embodiments each successive shell may comprise one or more strips ofconductor shaped so as to conform to the cylindrical geometry of thestructure. In embodiments the strips in each shell may be mutuallyinsulated and periodically connected to strips in adjacent shells sothat the input impedances of the shells and/or strips naturally enforcethe current distribution that minimizes the resistance of the structure.In embodiments the strips in each shell may be wound at a particularpitch. The pitch in different shells may be varied on as to assist inthe impedance matching of the entire structure.

FIG. 20 shows an end section of the conductor with the conducting layersstaggered to provide a clear illustration of the layers. The staggeringof layers in the drawing should not be considered as a preferredtermination of the conductor. The conductor comprising multiple shellsmay be terminated with all shells ending in the same plane or atdifferent staggered planes as depicted in FIG. 20.

In embodiments, the innermost conductor shell 2002 may be solid as shownin FIG. 20. In embodiments the innermost conductor shell may be hollowdefining a hole or cavity along its length along the z axis of theconductor.

In embodiments neighboring shells may be separated from each other bylayers of an electrical insulator such that neighboring layers are notin electrical contact with one another. The thickness and material ofthe insulating layer may depend on the voltages, currents, and relativevoltage potential between each neighboring shell. In general theinsulator should be selected such that its breakdown voltage exceeds thevoltage potential between neighboring conducting shells. In embodimentsthe outside of the outermost shell 2010 may be covered by additionalelectrical insulators or protective casing for electrical safety,durability, water resistance, and the like. In embodiments differentshells and insulator layers may have different thicknesses depending onthe application, frequency, power levels and the like.

Another view of a cross section of an embodiment of the conductorcomprising four shells is shown in FIG. 21. The figure shows across-section, normal to the z-axis, of the conductor comprising theconductor shells 2102, 2104, 2106, 2108. Note that in this figure, andin FIG. 20, the insulating layers are not shown explicitly, but areunderstood to be located between the various shells. In embodiments, thethickness of the insulating layers may be extremely thin, especially incomparison to the thickness of the conducting shells.

The thickness, relative thickness, size, composition, shape, number,fraction of total current carried and the like, of concentric conducingshells may be selected or optimized for specific criteria such as thevoltage and/or current levels carried by the wire, the operatingfrequency of the resonator, size, weight and flexibility requirements ofthe resonator, required Q-values, system efficiencies, costs and thelike. The appropriate size, number, spacing, and the like of theconductors may be determined analytically, through simulation, by trialand error, and the like.

The benefits of the concentric shell design may be seen by comparing thecurrent distributions in conductors of similar diameters but withdifferent conductor arrangements. By way of example, calculations of thecurrent distributions in two concentric shell conductor structures andone solid conductor are shown in FIGS. 22-24. The figures show onequarter of the cross section of the conductor with the conductor beingsymmetric around x=0, y=0 coordinate. The figures show the currentdensity at 10 MHz for a copper conductor with an outside diameter (OD)of 1 mm and carrying a peak current of 1 A. Note that the darkershadings indicate higher current densities, as shown in the legend onthe right hand side of the figure.

FIG. 22 shows the current distribution for a wire comprising a single, 1mm diameter, solid core of copper. Note that the current is concentratedon the outer perimeter of the solid conductor, limiting the area overwhich the current is distributed, and yielding an effective resistanceof 265.9 mΩ/m. This behavior is indicative of the known proximityeffect.

FIG. 23 shows the current distribution for an embodiment where the 1 mmdiameter wire comprises 24 mutually insulated 5.19 μm concentricconductive shells, around a solid innermost copper shell, totaling 25conductive shell elements. Note that the optimal current density (i.e.,the current distribution among the shells that minimizes the ACresistance, which may be found for any given structure usingmathematical techniques familiar to those skilled in the art) in thisstructure is more uniformly distributed, increasing the cross sectionover which the current flows, and reducing the effective resistance ofthe wire to 55.2 mΩ/m. Note that this wire comprising concentricconducting shells has an AC resistance that is approximately five timeslower than the similarly sized solid conducting wire.

FIG. 24 shows the current distribution for an embodiment where the 1 mmdiameter wire comprises 25 conductive shells (including an innermostsolid core) whose thicknesses are varied from shell to shell so as tominimize the overall resistance. Each shell is of a different thicknesswith thinner and thinner shells towards the outside of the wire. In thisembodiment, the thickness of the shells ranged from 16.3 μm to 3.6 μm(except for the solid innermost shell). The inset in FIG. 24 shows theradial locations of the interfaces between the shells. The effectiveresistance of the wire comprising the varying thickness shells as shownin FIG. 24 is 51.6 mΩ/m. Note that the resistance of the conductingstructures shown in FIGS. 22-24 was calculated analytically usingmethods described in A. Kurs, M. Kesler, and S. G. Johnson, Optimizeddesign of a low-resistance electrical conductor for the multimegahertzrange, Appl. Phys. Lett. 98, 172504 (2011), as well as U.S. ProvisionalApplication Ser. No. 61/411,490, filed Nov. 9, 2010 the contents of eachwhich are incorporated herein by reference in their entirety as if fullyset forth herein. For simplicity, the insulating gap between the shellswas taken to be negligibly small for each structure.

Note that while the embodiments modeled in FIGS. 23-24 comprised solidinnermost conductor shells, most of the current flowing in that shell isconfined to the outer layer of this innermost shell. In otherembodiments, this solid innermost shell may be replaced by a hollow orinsulator filled shell, a few skin-depths thick, without significantlyincreasing the AC resistance of the structure.

FIGS. 25-27 show plots that compare the ratio of the lowest ACresistance (as a function of the number of shells, N, and the operatingfrequency, f) achievable for a 1 mm OD wire comprising concentricconducting shells and a 1 mm OD solid core wire, of the same conductingmaterial.

FIG. 25 shows that an optimized cylindrical shell conductor cansignificantly outperform a solid conductor of the same OD. One can alsosee from FIG. 25 that much of the relative improvement of an optimizedconcentric shell conductor over a solid conductor occurs for structureswith only a small number of elements or shells. For example, a wirecomprising 10 concentric conducting shells has an AC resistance that isthree times lower than a similarly sized solid wire over the entire 2-20MHz range. Equivalently, since the resistance of a solid conductor inthe regime κD>>1 (κ being the inverse of the skin depth δ and D thediameter of the conductor) scales as 1/D, the conductor comprising tenshells would have the same resistance per unit length as a solidconductor with a diameter that is 3.33 times greater (and roughly 10times the cross area) than the wire comprising shells.

Increasing the number of shells to 20 and 30 further reduces the ACresistance to four times lower, and five times tower than the ACresistance for a similarly sized solid wire.

It should be noted that with the presented structures comprisingmultiple conductor shells it may be necessary to impedance match eachshell to ensure an optimal current distribution. However due to therelatively small number of shell conductors for most applications (<40)a brute force approach of individually matching the impedance of eachshell (e.g., with a lumped-element matching network) to achieve theoptimal current distribution could be implemented (similar impedancematching considerations arise in multi-layer high-T_(c) superconductingpower cables (see H. Noji, Supercond. Sci. Technol. 10, 552 (1997), andS. Mukoyama, K. Miyoshi, H. Tsubouti, T. Yoshida, M. Mimura, N. Uno, M.Ikeda, H. Ishii, S. Honjo, and Y. Iwata, IEEE Trans. Appl. Supercond. 9,1269 (1999), the contents of which are incorporated in their entirety asif fully set forth herein), albeit at much lower frequencies).

In embodiments, concentric conducting shells of a wire may preferably becylindrical or have circular cross-sections, however other shapes arecontemplated and may provide for substantial improvement over solidconductors. Concentric conducting shells having an elliptical,rectangular, triangular, or other irregular shapes are within the scopeof this invention. The practicality and usefulness of each cross-sectionshape may depend on the application, manufacturing costs, and the like.

In this section of the disclosure we may have referred to the structurescomprising multiple shells of conductors as a wire. It is to beunderstood that the term wire should not be limited to mean any specificor final form factor of the structures. In embodiments the structuresmay comprise free standing conductors that may be used to replacetraditional wires. In embodiments the structures comprising multipleshells may be fabricated or etched onto a multilayer printed circuitboard or substrate. The structures may be etched, deposited on wafers,boards, and the like. In embodiments thin concentric shells can befabricated by a variety of processes (such as electroplating,electro-deposition, vapor deposition, or processes utilized in opticalfiber fabrication).

The conductor structures may be utilized in many resonator or coilstructures used for wireless energy transfer. The multi-shell structuresmay be used as part of a resonator such as those shown in FIG. 2A-2E.The low loss conductors may be wrapped around a core of magneticmaterial to form low loss planar resonators. The low loss conductors maybe etched or printed on a printed circuit board to form a printed coiland the like.

Wireless Energy Distribution System

Wireless energy may be distributed over an area using repeaterresonators. In embodiments a whole area such as a floor, ceiling, wall,table top, surface, shelf, body, area, and the like may be wirelesslyenergized by positioning or tiling a series of repeater resonators andsource resonators over the area. In some embodiments, a group of objectscomprising resonators may share power amongst themselves, and power maybe wireless transmitted to and/or through various objects in the group.In an exemplary embodiment, a number of vehicles may be parked in anarea and only some of the vehicles may be positioned to receive wirelesspower directly from a source resonator. In such embodiments, certainvehicles may retransmit and/or repeat some of the wireless power tovehicles that are not parked in positions to receive wireless powerdirectly from a source. In embodiments, power supplied by a vehiclecharging source may use repeaters to transmit power into the vehicles topower devices such as cell phones, computers, displays, navigationdevices, communication devices, and the like. In some embodiments, avehicle parked over a wireless power source may vary the ratio of theamount of power it receives and the amount of power it retransmits orrepeats to other nearby vehicles. In embodiments, wireless power may betransmitted from one source to device after device and so on, in a daisychained fashion. In embodiments, certain devices may be able to selfdetermine how much power that receive and how much they pass on. Inembodiments, power distribution amongst various devices and/or repeatersmay be controlled by a master node or a centralized controller.

Some repeater resonators may be positioned in proximity to one or moresource resonators. The energy from the source may be transferred fromthe sources to the repeaters, and from those repeaters to otherrepeaters, and to other repeaters, and so on. Therefore energy may bewirelessly delivered to a relatively large area with the use of smallsized sources being the only components that require physical or wiredaccess to an external energy source.

In embodiments the energy distribution over an area using a plurality ofrepeater resonators and at least one source has many potentialadvantages including in ease of installation, configurability, control,efficiency, adaptability, cost, and the like. For example, using aplurality of repeater resonators allows easier installation since anarea may be covered by the repeater resonators in small increments,without requiring connections or wiring between the repeaters or thesource and repeaters. Likewise, a plurality of smaller repeater coilsallows a greater flexibility of placement allowing the arrangement andcoverage of an area with an irregular shape. Furthermore, the repeaterresonators may be easily moved or repositioned to change the magneticfield distribution within an area. In some embodiments the repeaters andthe sources may be tunable or adjustable allowing the repeaterresonators to be tuned or detuned from the source resonators andallowing a dynamic reconfiguration of energy transfer or magnetic fielddistribution within the area covered by the repeaters without physicallymoving components of the system.

For example, in one embodiment, repeater resonators and wireless energysources may be incorporated or integrated into flooring. In embodiments,resonator may be integrated into flooring or flooring products such ascarpet tiles to provide wireless power to an area, room, specificlocation, multiple locations and the like. Repeater resonators, sourceresonators, or device resonators may be integrated into the flooring anddistribute wireless power from one or more sources to one more deviceson the floor via a series of repeater resonators that transfer theenergy from the source over an area of the floor.

It is to be understood that the techniques, system design, and methodsmay be applied to many flooring types, shapes, and materials includingcarpet, ceramic tiles, wood boards, wood panels and the like. For eachtype of material those skilled in the art will recognize that differenttechniques may be used to integrate or attach the resonators to theflooring material. For example, for carpet tiles the resonators may besown in or glued on the underside while for ceramic tiles integration oftiles may require a slurry type material, epoxy, plaster, and the like.In some embodiments the resonators may not be integrated into theflooring material but placed under the flooring or on the flooring. Theresonators may, for example, come prepackaged in padding material thatis placed under the flooring. In some embodiments a series or an arrayor pattern of resonators, which may include source, device, and repeaterresonators, may be integrated in to a large piece of material orflooring which may be cut or trimmed to size. The larger material may betrimmed in between the individual resonators without disrupting ordamaging the operation of the cut piece.

Returning now to the example of the wireless floor embodiment comprisingindividual carpet tiles, the individual flooring tiles may be wirelesspower enabled by integrating or inserting a magnetic resonator to thetile or under the tile. In embodiments resonator may comprise a loop orloops of a good conductor such as Litz wire and coupled to a capacitiveelement providing a specific resonant frequency which may be in therange of 10 KHz to 100 MHz. In embodiments the resonator may be a high-Qresonator with a quality factor greater than 100. Those skilled in theart will appreciate that the various designs, shaped, and methods forresonators such as planar resonators, capacitively loaded loopresonators, printed conductor loops, and the like described herein maybe integrated or combined within a flooring tile or other flooringmaterial.

Example embodiments of a wireless power enabled floor tile are depictedin FIG. 28A and FIG. 28B. A floor tile 2802 may include loops of anelectrical conductor 2804 that are wound within the perimeter of thetile. In embodiments the conductor 2804 of the resonator may be coupledto additional electric or electronic components 2806 such as capacitors,power and control circuitry, communication circuitry, and the like. Inother embodiments the tile may include more than one resonator and morethan one loop of conductors that may be arranged in an array or adeliberate pattern as described herein such as for example a series ofmultisized coils, a configurable size coil and the like.

In embodiments the coils and resonators integrated into the tiles mayinclude magnetic material. Magnetic material may be used to constructplanar resonator structures such those depicted in FIG. 2C or FIG. 2E.In embodiments the magnetic material may also be used for shielding ofthe coil of the resonator from loamy objects that may be under or aroundthe flooring. In some embodiments the structures may further include alayer or sheet of a good electrical conductor under the magneticmaterial to increase the shielding capability of the magnetic materialas described herein.

Tiles with a resonator may have various functionalities and capabilitiesdepending on the control circuitry, communication circuitry, sensingcircuitry, and the like that is coupled to the coil or resonatorstructure. In embodiments of a wireless power enabled flooring thesystem may include multiple types of wireless enabled tiles withdifferent capabilities. One type of floor tile may comprise only amagnetic resonator and function as a fixed tuned repeater resonator thatwirelessly transfers power from one resonator to another resonatorwithout any direct or wired power source or wired power drain.

Another type of floor tile may comprise a resonator coupled to controlelectronics that may dynamically change or adjust the resonant frequencyof the resonator by, for example, adjusting the capacitance, inductance,and the like of the resonator. The tile may further include an in-bandor out-of-band communication capability such that it can exchangeinformation with other communication enabled tiles. The tile may be thenable to adjust its operating parameters such as resonant frequency inresponse to the received signals from the communication channel.

Another type of floor tile may comprise a resonator coupled tointegrated sensors that may include temperature sensors, pressuresensors, inductive sensors, magnetic sensors, and the like. Some or allthe power captured by the resonator may be used to wirelessly power thesensors and the resonator may function as a device or partially as arepeater.

Yet another type of wireless power enabled floor tile may comprise aresonator with power and control circuitry that may include an amplifierand a wired power connection for driving the resonator and function likea wireless power source. The features, functions, capabilities of eachof the tiles may be chosen to satisfy specific design constraints andmay feature any number of different combinations of resonators, powerand control circuitry, amplifiers, sensors, communication capabilitiesand the like.

A block diagram of the components comprising a resonator tile are shownin FIG. 29. In a tile, a resonator 2902 may be optionally coupled topower and control circuitry 2906 to receive power and power devices oroptional sensors 2904. Additional optional communication circuitry 2908may be connected to the power and control circuitry and control theparameters of the resonator based on received signals.

Tiles and resonators with different features and capabilities may beused to construct a wireless energy transfer systems with variousfeatures and capabilities. One embodiment of a system may includesources and only fixed tuned repeater resonator tiles. Another systemmay comprise a mixture of fixed and tunable resonator tiles withcommunication capability. To illustrate some of the differences insystem capabilities that may be achieved with different types of floortiles we will describe example embodiments of a wireless floor system.

The first example embodiment of the wireless floor system may include asource and only fixed tuned repeater resonator tiles. In this firstembodiment a plurality of fixed tuned resonator tiles may be arranged ona floor to transfer power from a source to an area or location over ornext to the tiles and deliver wireless power to devices that may beplaced on top of the tiles, below the tiles, or next to the tiles. Therepeater resonators may be fixed tuned to a fixed frequency that may beclose to the frequency of the source. An arrangement of the firstexample embodiment is shown in FIG. 30. The tiles 3002 are arranged inan array with at least one source resonator that may be integrated intoa tile 3010 or attached to a wall 3006 and wired 3012 to a power source.Some repeater tiles may be positioned next to the source resonator andarranged to transfer the power from the source to a desired location viaone or more additional repeater resonators.

Energy may be transferred to other tiles and resonators that are furtheraway from the source resonators using tiles with repeater resonatorswhich may be used to deliver power to devices, integrated or connectedto its own device resonator and device power and control electronicsthat are placed on top or near the tiles. For example, power from thesource resonator 3006 may be transferred wirelessly from the source 3006to an interior area or interior tile 3022 via multiple repeaterresonators 3014, 3016, 3018, 3020 that are between the interior tile3022 and the source 3006. The interior tile 3022 may than transfer thepower to a device such as a resonator built into the base of a lamp3008. Tiles with repeater resonators may be positioned to extend thewireless energy transfer to a whole area of the floor allowing a deviceon top of the floor to be freely moved within the area. For exampleadditional repeater resonator tiles 3024, 3026, 3028 may be positionedaround the lamp 3008 to create a defined area of power (tiles 3014,3016, 3018, 3020, 3022, 3024, 3026, 3028) over which the lamp may beplaced to receive energy from the source via the repeater tiles. Thedefined area over which power is distributed may be changed by addingmore repeater tiles in proximity to at least one other repeater orsource tile. The tiles may be movable and configurable by the user tochange the power distribution as needed or as the room configurationchanges. Except a few tiles with source resonators which may need wiredsource or energy, each tile may be completely wireless and may beconfigured or moved by the user or consumer to adjust the wireless powerflooring system.

A second embodiment of the wireless floor system may include a sourceand one or more tunable repeater resonator tiles. In embodiments theresonators in each or some of the tiles may include control circuitryallowing dynamic or periodic adjustment of the operating parameters ofthe resonator. In embodiments the control circuitry may change theresonant frequency of the resonator by adjusting a variable capacitor ora changing a bank of capacitors.

To obtain maximum efficiency of power transfer or to obtain a specificdistribution of power transfer in the system of multiple wireless powerenabled tiles it may be necessary to adjust the operating point of eachresonator and each resonator may be tuned to a different operatingpoint. For example, in some situations or applications the requiredpower distribution in an array of tiles may be required to benon-uniform, with higher power required on one end of the array andlower power on the opposite end of the array. Such a distribution may beobtained, for example, by slightly detailing the frequency of theresonators from the resonant frequency of the system to distribute thewireless energy where it is needed.

For example, consider the array of tiles depicted in FIG. 30 comprising36 tunable repeater resonator tiles with a single source resonator 3006.If only one device that requires power is placed on the floor, such asthe lamp 3008, it may be inefficient to distribute the energy acrossevery tile when the energy is needed in only one section of the floortile array. In embodiments the tuning of individual tiles may be used tochange the energy transfer distribution in the array. In the example ofthe single lamp device 3008, the repeater tiles that are not in directpath from the source resonator 3006 to the tile closes to the device3022 may be completely or partially detuned from the frequency of thesource. Detuning of the unused repeaters reduces the interaction of theresonators with the oscillating magnetic fields changing thedistribution of the magnetic fields in the floor area. With tunablerepeater tiles, a second device may be placed within the array of tilesor the lamp device 3008 is moved from its current location 3022 toanother tile, say 3030, the magnetic field distribution in the area ofthe tiles may be changed by retuning tiles that are in the path from thesource 3006 to the new location 3030.

In embodiments, to help coordinate the distribution of power and tuningof the resonators the resonator may include a communication capability.Each resonator may be capable of wirelessly communicating with one ormore of its neighboring tiles or any one of the tiles to establish anappropriate magnetic field distribution for a specific devicearrangement.

In embodiments the tuning or adjustment of the operating point of theindividual resonators to generate a desired magnetic field distributionover the area covered by the tiles may be performed in a centralizedmanner from one source or one “command tile”. In such a configurationthe central tile may gather the power requirements and the state of eachresonator and each tile via wireless communication or in bandcommunication of each tile and calculate the most appropriate operatingpoint of each resonator for the desired power distribution or operatingpoint of the system. The information may be communicated to eachindividual tile wirelessly by an additional wireless communicationchannel or by modulating the magnetic field used for power transfer. Thepower may be distributed or metered out using protocols similar to thoseused in communication systems. For example, there may be devices thatget guaranteed power, while others get best effort power. Power may bedistributed according to a greedy algorithm, or using a token system.Many protocols that have been adapted for sharing information networkresources may be adapted for sharing wireless power resources.

In other embodiments the tuning or adjustment of the operating point ofthe individual resonators may be performed in a decentralized manner.Each tile may adjust the operating point of its resonator on its ownbased on the power requirements or state of the resonators of tiles inits near proximity.

In both centralized and decentralized arrangements any number of networkbased centralized and distributed routing protocols may be used. Forexample, each tile may be considered as a node in network and shortestpath, quickest path, redundant path, and the like, algorithms may beused to determine the most appropriate tuning of resonators to achievepower delivery to one or more devices.

In embodiments various centralized and decentralized routing algorithmsmay be used to tune and detune resonators of a system to route power viarepeater resonators around lossy objects. If an object comprising lossymaterial is placed on some of the tiles it may the tiles, it mayunnecessarily draw power from the tiles or may disrupt energytransmission if the tiles are in the path between a source and thedestination tile. In embodiments the repeater tiles may be selectivelytuned to bypass lossy objects that may be on the tiles. Routingprotocols may be used to tune the repeater resonators such that power isrouted around lossy objects.

In embodiments the tiles may include sensors. The tiles may includesensors that may be power wirelessly from the magnetic energy capturedby the resonator built into the tile to detect objects, energy capturedevices, people 3034, and the like on the tiles. The tiles may includecapacitive, inductive, temperature, strain, weight sensors, and thelike. The information from the sensors may be used to calculate ordetermine the best or satisfactory magnetic field distribution todeliver power to devices and maybe used to detune appropriateresonators. In embodiments the tiles may comprise sensors to detectmetal objects. In embodiments the presence of a lossy object may bedetected by monitoring the parameters of the resonator. Lossy objectsmay affect the parameters of the resonator such as resonant frequency,inductance, and the like and may be used to detect the metal object.

In embodiments the wireless powered flooring system may have more thanone source and source resonators that are part of the tiles, that arelocated on the wall or in furniture that couple to the resonators in theflooring. In embodiments with multiple sources and source resonators thelocation of the sources may be used to adjust or change the powerdistribution within in the flooring. For example, one side of a room mayhave devices which require more power and may require more sourcescloser to the devices. In embodiments the power distribution in thefloor comprising multiple tiles may be adjusted by adjusting the outputpower (the magnitude of the magnetic field) of each source, the phase ofeach source (the relative phase of the oscillating magnetic field) ofeach source, and the like.

In embodiments the resonator tiles may be configured to transfer energyfrom more than one source via the repeater resonators to a device.Resonators may be tuned or detuned to route the energy from more thanone source resonator to more than one device or tile.

In embodiments with multiple sources it may be desirable to ensure thatthe different sources and maybe different amplifiers driving thedifferent sources are synchronized in frequency and/or phase. Sourcesthat are operating at slightly different frequencies and/or phase maygenerate magnetic fields with dynamically changing amplitudes andspatial distributions (due to beating effects between the oscillatingsources). In embodiments, Multiple source resonators may be synchronizedwith a wired or wireless synchronization signal that may be generated bya source or external control unit. In some embodiments one sourceresonator may be designed as a master source resonator that dictates thefrequency and phase to other resonators. A master resonator may operateat its nominal frequency while other source resonators detect thefrequency and phase of the magnetic fields generated by the mastersource and synchronize their signals with that of the master.

In embodiments the wireless power from the floor tiles may betransferred to table surfaces, shelves, furniture and the like byintegrating additional repeater resonators into the furniture and tablesthat may extend the range of the wireless energy transfer in thevertical direction from the floor. For example, in some embodiments of awireless power enabled floor, the power delivered by the tiles may notbe enough to directly charge a phone or an electronic device that may beplaced on top of a table surface that may be two or three feet above thewireless power enabled tiles. The coupling between the small resonatorof the electronic device on the surface of the table and the resonatorof the tile may be improved by placing a large repeater resonator nearthe surface of the table such as on the underside of the table. Therelatively large repeater resonator of the table may have good couplingwith the resonator of the tiles and, due to close proximity, goodcoupling between the resonator of the electronic device on the surfaceof the table resulting in improved coupling and improved wireless powertransfer between the resonator of the tile and the resonator of thedevice on the table.

As those skilled in the art will recognize the features and capabilitiesof the different embodiments described may be rearranged or combinedinto other configurations. A system may include any number of resonatortypes, source, devices, and may be deployed on floors, ceilings, walls,desks, and the like. The system described in terms of floor tiles may bedeployed onto, for example, a wall and distribute wireless power on awall or ceiling into which enabled devices may be attached or positionedto receive power and enable various applications and configurations. Thesystem techniques may be applied to multiple resonators distributedacross table tops, surfaces, shelves, bodies, vehicles, machines,clothing, furniture, and the like. Although the example embodimentsdescribed tiles or separate repeater resonators that may be arrangedinto different configurations based on the teachings of this disclosureit should be clear to those skilled in the art that multiple repeater orsource resonator may not be attached or positioned on separate physicaltiles or sheets. Multiple repeater resonators, sources, devices, andtheir associated power and control circuitry may be attached, printed,etched, to one tile, sheet, substrate, and the like. For example, asdepicted in FIG. 31, an array of repeater resonators 3104 may beprinted, attached, or embedded onto one single sheet 3102. The singlesheet 3102 may be deployed similarly as the tiles described above. Thesheet of resonators may be placed near, on, or below a source resonatorto distribute the wireless energy through the sheet or parts of thesheet. The sheet of resonators may be used as a configurable sizedrepeater resonator in that the sheet may be cut or trimmed between thedifferent resonators such as for example along line 3106 shown in FIG.31.

In embodiments a sheet of repeater resonators may be used in a desktopenvironment. Sheet of repeater resonators may be cut to size to fit thetop of a desk or part of the desk, to fit inside drawers, and the like.A source resonator may be positioned next to or on top of the sheet ofrepeater resonators and devices such as computers, computer peripherals,portable electronics, phones, and the like may be charged or powered viathe repeaters.

In embodiments resonators embedded in floor tiles or carpets can be usedto capture energy for radiant floor heating. The resonators of each tilemay be directly connected to a highly resistive heating element viaunrectified AC, and with a local thermal sensor to maintain certainfloor temperature. Each tile may be able to dissipate a few watts ofpower in the thermal element to heat a room or to maintain the tiles ata specific temperature.

While the invention has been described in connection with certainpreferred embodiments, other embodiments will be understood by one ofordinary skill in the art and are intended to fall within the scope ofthis disclosure, which is to be interpreted in the broadest senseallowable by law.

All documents referenced herein are hereby incorporated by reference intheir entirety as if fully set forth herein.

1. A system for wireless energy distribution over a defined area, thesystem comprising: a source resonator coupled to an energy source andgenerating an oscillating magnetic field with a frequency, at least onerepeater resonator positioned in a defined area and in proximity to thesource resonator, and having a resonant frequency; and at least twoother repeater resonators with a resonant frequency positioned in thedefined area and in proximity to at least one of the repeaterresonators, wherein the repeater resonators provide an effectivewireless energy transfer area at least one of within or equal to thedefined area.
 2. The system of claim 1, wherein the defined area coveredis at least 2 square meters.
 3. The system of claim 1, wherein thedefined area covered is at east 10 square centimeters.
 4. The system ofclaim 1 further comprising at least one additional source resonator thatgenerates an oscillating magnetic field with the frequency, wherein theat least one additional source resonator is positioned in proximity todefined area.
 5. The system of claim 4, wherein the frequency andrelative phase of the oscillating fields generated by the sources of thesystem are synchronized.
 6. The system of claim 4, wherein the relativephase of the oscillating fields generated by the different sources ofthe system is adjustable.
 7. The system of claim 4, wherein at least onerepeater resonator comprises a capacitively loaded conducting loop. 8.The system of claim 4, wherein at least one of the repeater resonatorshave an adjustable resonant frequency.
 9. The system of claim 8, whereinthe resonant frequency of the repeater resonators may be detuned fromthe frequency of the magnetic fields generated by the source resonatorsto change the distribution of the magnetic fields in the defined area.10. The system of claim 9, wherein some repeaters are detuned tomaximize the magnetic fields in a region of the defined area.
 11. Thesystem of claim 10, wherein the detuning of repeaters is performedaccording to a network routing algorithm.
 12. The system of claim 10,further comprising a communication channel between the resonators of thesystem.
 13. The system of claim 12, wherein the communication channel isused to coordinate detuning of the repeater resonators of the system toachieve a specific magnetic field distribution.
 14. The system of claim1, wherein the repeater resonators have a quality factor Q>100.
 15. Thesystem of claim 10, wherein the repeater resonators further comprisepressure sensors and wherein the information from the pressure sensorsis used to change the magnetic field distribution.
 16. The system ofclaim 1, wherein the defined area is a floor
 17. The system of claim 16,wherein the resonators are integrated into flooring material.
 18. Thesystem of claim 1, wherein the defined area is a wall.
 19. The system ofclaim 1, wherein the defined area is a ceiling.
 20. A wireless energytransfer flooring system comprising: at least one source resonatorcoupled to an energy source and generating an oscillating magnetic fieldwith a frequency, at least one repeater resonator positioned in adefined area and in proximity to the source resonator, and having atunable resonant frequency; and at least two other repeater resonatorswith a tunable resonant frequency positioned in the defined area and inproximity to at least one other of the repeater resonators, wherein theresonant frequency of at least one of the repeater resonators is detunedfrom the frequency of the oscillating magnetic field of the at least onesource to change the distribution of magnetic fields in the definedarea.
 21. The system of claim 20, further comprising a communicationchannel between the resonators of the system.
 22. The system of claim21, wherein the communication channel is used to coordinate detuning ofthe repeater resonators of the system to achieve a specific magneticfield distribution.
 23. The system of claim 20, wherein the resonatorsare integrated into flooring material.
 24. A method of distributingwireless energy from at least one source resonator to a specificlocation within an area having tunable repeater resonators, the methodcomprising: determining a closest repeater resonators to the specificlocation, and tuning the resonant frequency of the repeater resonatorsto provide for an energy transfer path from the source to the closestrepeater resonators.
 25. The method of claim 24, further comprisingdetuning resonators that are not in the energy transfer path.
 26. Themethod of claim 24, wherein the energy transfer path is determined by ashortest path algorithm.
 27. The method of claim 24, wherein the energytransfer path is determined by a central control.